---
title: CSCI 1100 - Test 2 Overview and Practice Questions
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date: 2024-03-15T00:13:02-04:00
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description: This blog post provides an overview of Test 2 for CSCI 1100 - Computer Science 1, including important logistical instructions, topics covered, and practice questions with solutions to help students prepare for the exam.
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summary: This blog post provides an overview of Test 2 for CSCI 1100 - Computer Science 1, including important logistical instructions, topics covered, and practice questions with solutions to help students prepare for the exam.
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# See details front matter: https://fixit.lruihao.cn/documentation/content-management/introduction/#front-matter
---

<!--more-->

## Important Logistical Instructions:

- Test 2 will be held Thursday, March 14, 2024.
- Most students will take the exam from 6:00 - 7:30 pm. Students who provided us with an accommodation letter indicating the need for extra time or a quiet location will be given a separate room and may be allowed to continue past 7:30.
- Room assignments will be posted on Submitty by the Wednesday night before the exam, March 13th.
- Students MUST:
   - Go to their assigned rooms.
   - Bring their IDs to the exam.
   - Sit in the correct section.
   - Put away all calculators, phones, etc. and take off/out all headphones and earbuds

Failing to do one of these may result in a 20 point penalty on the exam score. Failure to do all can cost up to 80 points.

- You cannot leave the exam room (not even for a bathroom break) until you hand over your exam.
- Similar to exam 1, a one-page crib-sheet is allowed during the test.

## Overview

### Exam Coverage

The primary coverage for this exam includes Lectures 7-13, Labs 3-6, and Homework 2-5. Material from tuples and modules are also part of this test. However, images will not be covered.

### Important Topics

1. Lists and tuples: Be comfortable with list functions (append, insert, remove, concatenation, replication, and slicing) and understand the differences between tuples, strings, and lists.
2. Control structures: Study the use of if statements, while and for loops, ranges, splitting, and slicing.
3. Basic list operations: Learn to compare items from two separate lists, find specific items in a list, find the index of a specific item in a list (min, max, last value with some property), and add up values in a list.
4. Functions over lists: Write functions to check if a list contains a specific type of item (e.g., negative, 0, divisible by 3) and return True or False accordingly.
5. Booleans and comparisons: Know booleans, comparisons, and the boolean functions and, or, and not. Be able to generate truth tables for boolean expressions.
6. File operations: Know how to read data from files and perform other file operations.

### Grids (List of Lists)

Get comfortable working with grids (list of lists). Know how to print a grid using nested loops and practice checking neighbors of a given element in a list of lists. Review these concepts by re-reading/re-writing your solutions for homework 5.

### Previous Material

While the exam will focus on the material above, questions may be asked about any material from previous labs, lectures, and homeworks. Make sure you understand the difference between printing a value in a function, returning a value from a function, or both printing and returning.

### Exam Rules

No calculators, textbooks, class notes, smart watches, or electronics of any kind are allowed. However, you may bring a one-page, double-sided, 8.5" x 11" "crib sheet" that you can prepare as you wish, even in groups. Each student must have their own copy during the test and turn it in with the exam.

### Sample Questions and Solutions

Many sample questions, more than will be on the test, are provided. Solutions to most of the problems will be posted online in the Course Resources section of Submitty, except for problems involving output from Python, which you should test yourself. Your solution to any question requiring Python code will be at most 10-15 lines long, and may be much shorter. The test questions will be closely related to these practice problems and problems from the homework, labs, and lecture exercises.

### Additional Tips

1. Syntax will be less important on this test than on the previous test, but do not ignore it entirely.
2. Learn to read and follow code to develop your debugging skills and understanding of

## Questions

### Compare Date

> Write a Python function called compare date that takes as arguments two lists of two integers each. Each list contains a month and a year, in that order. The function should return -1 if the first month and year are earlier than the second month and year, 0 if they are the same, and 1 if the first month and year are later than the second. Your code should work for any legal input for month and year. Example calls and expected output are shown below:
> 
> ```python
> >>> compare_date( [10,1995], [8,1995] )
> 1
> >>> compare_date( [5,2010], [5,2010] )
> 0
> >>> compare_date( [10,1993], [8,1998] )
> -1
> ```

{{< details summary="**Answer of This Question**" >}}
Here's a Python function that compares two dates given as lists of month and year and returns -1, 0, or 1 based on their order:

```python
def compare_date(date1, date2):
    month1, year1 = date1
    month2, year2 = date2
    
    if year1 < year2:
        return -1
    elif year1 > year2:
        return 1
    else:
        if month1 < month2:
            return -1
        elif month1 > month2:
            return 1
        else:
            return 0
```

Explanation:

1. The function `compare_date` takes two arguments, `date1` and `date2`, which are lists containing the month and year of each date.

2. We unpack the month and year from each date list into separate variables: `month1`, `year1`, `month2`, and `year2`.

3. We first compare the years:
   - If `year1` is less than `year2`, we return -1 since the first date is earlier.
   - If `year1` is greater than `year2`, we return 1 since the first date is later.
   - If `year1` is equal to `year2`, we move on to compare the months.

4. If the years are the same, we compare the months:
   - If `month1` is less than `month2`, we return -1 since the first date is earlier.
   - If `month1` is greater than `month2`, we return 1 since the first date is later.
   - If `month1` is equal to `month2`, we return 0 since the dates are the same.

The function correctly handles any legal input for month and year. It compares the years first, and if they are the same, it compares the months to determine the order of the dates.

You can test the function with the provided example calls:

```python
print(compare_date([10, 1995], [8, 1995]))  # Output: 1
print(compare_date([5, 2010], [5, 2010]))   # Output: 0
print(compare_date([10, 1993], [8, 1998]))  # Output: -1
```

The function will return the expected output for each example call.
{{< /details >}}

### Highest Two Values

> Assume v is a list containing numbers. Write Python code to find and print the highest two values in v. If the list contains only one number, print only that number. If the list is empty, print nothing. For example, if we assigned
> 
> ```python
> v = [ 7, 3, 1, 5, 10, 6 ]
> ```
> 
> then the output of your code should be something like
> 
> ```python
> 7 10
> ```
> 
> If we are given that
> 
> ```python
> v = [ 7 ]
> ```
> 
> then the output of your code should be
> 
> ```python
> 7
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the Python code to find and print the highest two values in a list `v`:

```python
if len(v) >= 2:
    highest = max(v)
    v.remove(highest)
    second_highest = max(v)
    print(second_highest, highest)
elif len(v) == 1:
    print(v[0])
```

Explanation:

1. We start by checking the length of the list `v` using the `len()` function.

2. If the length of `v` is greater than or equal to 2, it means there are at least two elements in the list. In this case:
   - We find the highest value in the list using the `max()` function and store it in the variable `highest`.
   - We remove the highest value from the list using the `remove()` method. This is done to find the second highest value.
   - We find the second highest value in the updated list using `max()` again and store it in the variable `second_highest`.
   - Finally, we print the `second_highest` and `highest` values separated by a space.

3. If the length of `v` is equal to 1, it means there is only one element in the list. In this case:
   - We simply print the only element in the list, which is accessed using `v[0]`.

4. If the length of `v` is 0 (i.e., the list is empty), the code will not execute any of the conditions, and nothing will be printed.

Examples:

1. If `v = [7, 3, 1, 5, 10, 6]`, the output will be:
   ```
   7 10
   ```

2. If `v = [7]`, the output will be:
   ```
   7
   ```

3. If `v = []` (an empty list), no output will be generated.

This code efficiently finds and prints the highest two values in the list, handles the case when there is only one element, and does nothing if the list is empty.
{{< /details >}}

### Italian Restaurants

> Consider a simplified version of the lab Yelp data, where just the name of the restaurant, the type of restaurant, and the ratings are provided. Assume these values have already been read into a list of lists of the form below:
> 
> ```python
> restaurants = [ 
>     [ 'Acme', 'Italian', 2, 4, 3, 5],
>     [ 'Flintstone', 'Steak', 5, 2, 4, 3, 3, 4],
>     [ 'Bella Troy', 'Italian', 1, 4, 5] 
> ]
> ```
> 
> Write a segment of Python code that prints all Italian restaurants in the `restaurants` list that have no ratings of value 1 and at least one rating of value 5. In the above example, `Acme` would be printed in the output, but `Flintstone` and `Bella Troy` would not. `Flintstone` is not Italian and `Bella Troy` has a 1 rating. Your code should work for any legal version of `restaurants`.

{{< details summary="**Answer of This Question**" >}}
Here's the Python code that prints all Italian restaurants in the `restaurants` list that have no ratings of value 1 and at least one rating of value 5:

```python
for restaurant in restaurants:
    if restaurant[1] == 'Italian' and 1 not in restaurant[2:] and 5 in restaurant[2:]:
        print(restaurant[0])
```

Explanation:

1. We start by iterating over each restaurant in the `restaurants` list using a `for` loop. Each restaurant is represented as a sublist within the `restaurants` list.

2. Inside the loop, we check three conditions using an `if` statement:
   - `restaurant[1] == 'Italian'`: This condition checks if the second element of the current restaurant sublist is equal to the string 'Italian'. This ensures that we are only considering Italian restaurants.
   - `1 not in restaurant[2:]`: This condition checks if the value 1 is not present in the ratings of the current restaurant. We use slicing (`restaurant[2:]`) to consider only the ratings, which start from the third element of the sublist.
   - `5 in restaurant[2:]`: This condition checks if the value 5 is present in the ratings of the current restaurant. Again, we use slicing to consider only the ratings.

3. If all three conditions are satisfied for a restaurant, it means that the restaurant is Italian, has no ratings of value 1, and has at least one rating of value 5. In this case, we print the name of the restaurant, which is the first element of the restaurant sublist (`restaurant[0]`).

4. The loop continues to the next restaurant in the `restaurants` list until all restaurants have been checked.

Using the example `restaurants` list provided:

```python
restaurants = [
    ['Acme', 'Italian', 2, 4, 3, 5],
    ['Flintstone', 'Steak', 5, 2, 4, 3, 3, 4],
    ['Bella Troy', 'Italian', 1, 4, 5]
]
```

The output of the code will be:
```
Acme
```

Only 'Acme' is printed because it is an Italian restaurant with no ratings of value 1 and at least one rating of value 5. 'Flintstone' is not Italian, and 'Bella Troy' has a rating of value 1, so they are not printed.

This code will work for any valid `restaurants` list that follows the specified format.
{{< /details >}}

### High Average Rating Restaurants

> Continuing with the Yelp data, assume that you have the code
> 
> ```python
> in_file = open('yelp.txt')
> for line in in_file:
>     p_line = parse_line(line)
>     print(p_line)
> ```
> 
> and that the `parse_line` function will return a list that looks like
> 
> ```python
> ["Meka's Lounge", 42.74, -73.69, "Bars", [5, 2, 4, 4, 3, 4, 5], 3.857 ]
> ```
> 
> where the last entry in the list is the average rating. Modify the for loop above to create a list called `high` that stores the names of all restaurants that have an average rating of at least 4.0. You do not have to print `high`.

{{< details summary="**Answer of This Question**" >}}
To create a list called `high` that stores the names of all restaurants with an average rating of at least 4.0, you can modify the `for` loop as follows:

```python
in_file = open('yelp.txt')
high = []
for line in in_file:
    p_line = parse_line(line)
    if p_line[-1] >= 4.0:
        high.append(p_line[0])
```

Explanation:

1. Before the `for` loop, we initialize an empty list called `high` to store the names of the restaurants with high average ratings.

2. Inside the `for` loop, we parse each line of the file using the `parse_line` function, which returns a list `p_line` with the restaurant's information.

3. We check if the last element of `p_line` (i.e., `p_line[-1]`), which represents the average rating, is greater than or equal to 4.0 using the condition `if p_line[-1] >= 4.0`.

4. If the condition is true, it means the restaurant has an average rating of at least 4.0. In this case, we append the name of the restaurant, which is the first element of `p_line` (i.e., `p_line[0]`), to the `high` list using `high.append(p_line[0])`.

5. The loop continues to the next line in the file until all lines have been processed.

After the loop finishes, the `high` list will contain the names of all restaurants with an average rating of at least 4.0.

For example, if the `yelp.txt` file contains the following lines:
```
Meka's Lounge,42.74,-73.69,Bars,[5,2,4,4,3,4,5],3.857
Joe's Diner,40.71,-74.01,American,[4,3,5,4,4,5],4.167
Sushi Spot,37.78,-122.41,Japanese,[4,4,5,3,4,4,5],4.143
```

After running the modified code, the `high` list will contain:
```python
['Joe's Diner', 'Sushi Spot']
```

These are the names of the restaurants with an average rating of at least 4.0.

Note that we don't print the `high` list in the code as per the requirement. The list will be available for further use if needed.
{{< /details >}}

### Chess Score

> In the game of chess you can often estimate how well you are doing by adding the values of the pieces you have captured. The pieces are Pawns, Bishops, Knights, Rooks and Queens. Their values are
> 
> ```text
> P - (P)awn, value = 1
> B - (B)ishop, value = 3
> K - (K)night, value = 3
> R - (R)ook, value = 5
> Q - (Q)ueen, value = 9
> ```
> 
> Write a Python function called `chess_score` that takes a single string as an argument and returns the combined values represented by the pieces in the string. You may assume that only 'P', 'B', 'K', 'R', and 'Q' appear in the string. You may not use any if statements and you may not use any loops. As an example,
> 
> ```python
> print(chess_score('BQBP'))
> ```
> 
> should output the value 16 because there are 2 Bishops (3 points each), 1 Queen (9 points each), and 1 Pawn (1 point each).

{{< details summary="**Answer of This Question**" >}}
Here's a Python function `chess_score` that calculates the combined values of the chess pieces represented by a string without using any `if` statements or loops:

```python
def chess_score(pieces):
    return pieces.count('P') + pieces.count('B') * 3 + pieces.count('K') * 3 + pieces.count('R') * 5 + pieces.count('Q') * 9
```

Explanation:

1. The function `chess_score` takes a single string `pieces` as an argument, which represents the captured chess pieces.

2. To calculate the score, we use the `count()` method of the string to count the occurrences of each piece and multiply it by its corresponding value:
   - `pieces.count('P')`: Counts the number of Pawns ('P') in the string and multiplies it by 1 (the value of a Pawn).
   - `pieces.count('B') * 3`: Counts the number of Bishops ('B') in the string and multiplies it by 3 (the value of a Bishop).
   - `pieces.count('K') * 3`: Counts the number of Knights ('K') in the string and multiplies it by 3 (the value of a Knight).
   - `pieces.count('R') * 5`: Counts the number of Rooks ('R') in the string and multiplies it by 5 (the value of a Rook).
   - `pieces.count('Q') * 9`: Counts the number of Queens ('Q') in the string and multiplies it by 9 (the value of a Queen).

3. The function returns the sum of all the calculated values, which represents the total score of the captured pieces.

Example usage:

```python
print(chess_score('BQBP'))
```

Output:
```
16
```

Explanation:
- The string 'BQBP' contains 2 Bishops ('B'), 1 Queen ('Q'), and 1 Pawn ('P').
- The score is calculated as follows:
  - 2 Bishops * 3 points each = 6 points
  - 1 Queen * 9 points each = 9 points
  - 1 Pawn * 1 point each = 1 point
- The total score is 6 + 9 + 1 = 16.

This function calculates the chess score based on the captured pieces represented by the input string without using any `if` statements or loops. It utilizes the `count()` method to count the occurrences of each piece and multiplies them by their respective values to obtain the total score.
{{< /details >}}

### Sum Integers from File

> You are given a file that contains, on each line of input, three integers separated by commas. Write a Python program that sums all of the first integers, the second integers, and the third integers, outputting the resulting sums all on one line, separated by commas. As a simple example, if the input is
> 
> ```python
> 2, 5,7
> 3, 6, 10
> 1, 2, -3
> 2, 4, 1
> ```
> 
> Then the output should be
> 
> ```python
> 8, 17, 15
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the Python program that reads integers from a file, sums them based on their positions, and outputs the resulting sums:

```python
# Open the file for reading
with open('input.txt', 'r') as file:
    # Initialize variables to store the sums
    sum1 = 0
    sum2 = 0
    sum3 = 0
    
    # Read each line from the file
    for line in file:
        # Split the line into individual integers
        integers = line.strip().split(',')
        
        # Convert the integers to int and add them to the respective sums
        sum1 += int(integers[0])
        sum2 += int(integers[1])
        sum3 += int(integers[2])
    
    # Print the resulting sums separated by commas
    print(f"{sum1}, {sum2}, {sum3}")
```

Explanation:

1. We start by opening the file named 'input.txt' for reading using the `with` statement. This ensures that the file is properly closed after we're done reading from it.

2. We initialize three variables `sum1`, `sum2`, and `sum3` to store the sums of the first, second, and third integers, respectively.

3. We use a `for` loop to read each line from the file. The `file` object is iterable, so we can directly iterate over its lines.

4. For each line, we use the `strip()` method to remove any leading or trailing whitespace, and then we use the `split(',')` method to split the line into individual integers based on the comma separator. This gives us a list of strings representing the integers.

5. We convert each integer string to an actual integer using the `int()` function and add it to the respective sum variable (`sum1`, `sum2`, or `sum3`) based on its position in the line.

6. After processing all the lines, we have the final sums stored in `sum1`, `sum2`, and `sum3`.

7. Finally, we use the `print()` function to output the resulting sums separated by commas. We use an f-string to format the output, where `{sum1}`, `{sum2}`, and `{sum3}` are placeholders for the actual sum values.

Make sure to save the input data in a file named 'input.txt' in the same directory as the Python script. When you run the script, it will read the integers from the file, calculate the sums, and output the resulting sums separated by commas.
{{< /details >}}

### Generate Ranges

> Write a single line of Python code to generate the following ranges
> 
> (a) [100, 99, 98, . . . , 0]  
> (b) [55, 53, 51, . . . ,−1]  
> (c) [3, 5, 7, 9, . . . , 29]  
> (d) [−95,−90,−85, . . . , 85, 90]
> 
> Now do it using a loop. For the loop, you can assume the list will be in the variable `L` at the end.

{{< details summary="**Answer of This Question**" >}}
Single line of Python code to generate the ranges:

(a) `list(range(100, -1, -1))`  
(b) `list(range(55, -2, -2))`  
(c) `list(range(3, 30, 2))`  
(d) `list(range(-95, 91, 5))`

Using a loop to generate the ranges:

(a)
```python
L = []
for i in range(100, -1, -1):
    L.append(i)
```

(b)
```python
L = []
for i in range(55, -2, -2):
    L.append(i)
```

(c)
```python
L = []
for i in range(3, 30, 2):
    L.append(i)
```

(d)
```python
L = []
for i in range(-95, 91, 5):
    L.append(i)
```

Explanation:

1. Single line of Python code:
   - We use the `range()` function to generate the desired range of numbers.
   - The `range()` function takes three arguments: start, stop, and step.
     - start: The starting number of the range (inclusive).
     - stop: The ending number of the range (exclusive).
     - step: The difference between each number in the range.
   - We wrap the `range()` function with the `list()` function to convert the range object into a list.

2. Using a loop:
   - We initialize an empty list `L` to store the numbers.
   - We use a `for` loop to iterate over the desired range of numbers.
   - Inside the loop, we use the `append()` method to add each number to the list `L`.
   - The loop parameters are the same as the `range()` function arguments:
     - start: The starting number of the range (inclusive).
     - stop: The ending number of the range (exclusive).
     - step: The difference between each number in the range.

Both approaches generate the same ranges of numbers. The single line of code is more concise, while the loop approach allows for more flexibility and customization if needed.
{{< /details >}}

### Sum Until Negative

> Write a while loop to add all of the numbers in a list `v` until it reaches a negative number or until it reaches the end of the list. Store the sum in the variable `result`. Your code should work for any version of `v` containing only numbers. For example, the value of `result` should be 25 after the loop for both of the following lists:
> 
> ```python
> v = [ 10, 12, 3, -5, 5, 6 ]
> v = [ 0, 10, 3, 6, 5, 1 ]
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the Python code that uses a while loop to add all the numbers in a list `v` until it reaches a negative number or the end of the list:

```python
i = 0
result = 0

while i < len(v) and v[i] >= 0:
    result += v[i]
    i += 1
```

Explanation:

1. We initialize two variables:
   - `i`: It serves as the index variable to keep track of the current position in the list `v`. It starts from 0, representing the first element of the list.
   - `result`: It stores the sum of the numbers. It is initialized to 0.

2. We start a while loop with two conditions:
   - `i < len(v)`: This condition checks if the index `i` is within the bounds of the list `v`. It ensures that we don't go beyond the last element of the list.
   - `v[i] >= 0`: This condition checks if the current element at index `i` is non-negative. It ensures that we stop adding numbers when we encounter a negative number.

3. Inside the loop:
   - We add the current element at index `i` to the `result` variable using the `+=` operator. This accumulates the sum of the numbers.
   - We increment the index `i` by 1 using `i += 1` to move to the next element in the list.

4. The loop continues until either of the conditions becomes false:
   - If `i` becomes equal to or greater than `len(v)`, it means we have reached the end of the list, and the loop terminates.
   - If the current element at index `i` is negative (`v[i] < 0`), the loop terminates.

5. After the loop ends, the `result` variable will contain the sum of all the numbers in the list `v` until a negative number is encountered or the end of the list is reached.

Let's test the code with the given examples:

Example 1:
```python
v = [10, 12, 3, -5, 5, 6]
```
After the loop, `result` will be 25 because the loop stops when it reaches the negative number -5.

Example 2:
```python
v = [0, 10, 3, 6, 5, 1]
```
After the loop, `result` will also be 25 because the loop adds all the numbers until it reaches the end of the list.

The code works correctly for any list `v` containing only numbers, and it stops adding numbers when it encounters a negative number or reaches the end of the list.
{{< /details >}}

### Positive Values in Increasing Order

> Write Python code that takes a list of numbers, `v`, and outputs the positive values that are in `v` in increasing order, one value per line. If there are no positive values, then the output should be the string 'None'. You may assume there is at least one value in the list. As an example,
> 
> ```python
> v = [ 17, -5, 15, -3, 12, -5, 0, 12, 22, -1 ]
> ```
> 
> Then the output of your code should be
> 
> ```python
> 12
> 12
> 15
> 17
> 22
> ```
> 
> As a second example, if
> 
> ```python
> v = [ -17, -5, -15, -3, -12, -5, 0, -12, -22, -1 ]
> ```
> 
> then then output should be just
> 
> ```python
> None
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the Python code that takes a list of numbers, `v`, and outputs the positive values in increasing order, one value per line, or 'None' if there are no positive values:

```python
positive_values = sorted(filter(lambda x: x > 0, v))

if positive_values:
    for value in positive_values:
        print(value)
else:
    print('None')
```

Explanation:

1. We use the `filter()` function to create an iterator that contains only the positive values from the list `v`. The `lambda` function `lambda x: x > 0` is used as the filtering condition, which returns `True` for values greater than 0 (positive values).

2. We pass the iterator returned by `filter()` to the `sorted()` function, which sorts the positive values in ascending order. The result is stored in the `positive_values` list.

3. We use an `if-else` statement to check if there are any positive values in the `positive_values` list:
   - If `positive_values` is not empty (evaluates to `True`), it means there are positive values in the list.
     - We use a `for` loop to iterate over each value in `positive_values`.
     - Inside the loop, we use the `print()` function to output each positive value on a separate line.
   - If `positive_values` is empty (evaluates to `False`), it means there are no positive values in the list.
     - We use the `print()` function to output the string 'None'.

Let's test the code with the given examples:

Example 1:
```python
v = [17, -5, 15, -3, 12, -5, 0, 12, 22, -1]
```
Output:
```
12
12
15
17
22
```

Example 2:
```python
v = [-17, -5, -15, -3, -12, -5, 0, -12, -22, -1]
```
Output:
```
None
```

The code correctly outputs the positive values in increasing order, one value per line, for the first example. For the second example, where there are no positive values, it outputs 'None'.

Note: The code assumes that there is at least one value in the list `v`, as mentioned in the problem statement.
{{< /details >}}

### List Operations Output

> What is the output of the following operations:
> 
> ```python
> >>> mylist = [1,4,8,12,6]
> >>> x = mylist.sort()
> >>> print(x)
> 
> >>> mylist = [1,4,8,12,6]
> >>> slice1 = mylist[2:4]
> >>> slice1[0] = 20
> >>> print(slice1)
> 
> >>> print(mylist)
> ```

{{< details summary="**Answer of This Question**" >}}
The output of the given operations will be as follows:

Operation 1:
```python
>>> mylist = [1,4,8,12,6]
>>> x = mylist.sort()
>>> print(x)
```
Output:
```
None
```

Explanation:
- The `sort()` method sorts the list `mylist` in place, modifying the original list.
- The `sort()` method returns `None`, not the sorted list.
- When you assign the result of `mylist.sort()` to `x`, `x` becomes `None`.
- Printing `x` outputs `None`.

Operation 2:
```python
>>> mylist = [1,4,8,12,6]
>>> slice1 = mylist[2:4]
>>> slice1[0] = 20
>>> print(slice1)
```
Output:
```
[20, 12]
```

Explanation:
- `mylist[2:4]` creates a new list `slice1` containing elements from index 2 to 3 (exclusive) of `mylist`.
- `slice1` is a separate list from `mylist`, and modifying `slice1` does not affect `mylist`.
- `slice1[0] = 20` assigns the value 20 to the first element of `slice1`.
- Printing `slice1` outputs `[20, 12]`.

Operation 3:
```python
>>> print(mylist)
```
Output:
```
[1, 4, 8, 12, 6]
```

Explanation:
- `mylist` remains unchanged from its original state `[1, 4, 8, 12, 6]`.
- The modifications made to `slice1` in Operation 2 do not affect `mylist`.
- Printing `mylist` outputs `[1, 4, 8, 12, 6]`.

In summary:
- Operation 1 outputs `None` because `sort()` modifies the list in place and returns `None`.
- Operation 2 outputs `[20, 12]` because `slice1` is a separate list, and modifying it does not affect `mylist`.
- Operation 3 outputs `[1, 4, 8, 12, 6]` because `mylist` remains unchanged from its original state.
{{< /details >}}

### Function Output

> What is the output of the following program?
> 
> ```python
> def spam(a1,b1,a2,b2):
>     if (a1 == a2) and (b1 > b2):
>         return 1
>     else:
>         return 0
> 
> def egg(a1,b1,a2,b2):
>     if (a1 > a2) and (b1 == b2):
>         return 0
>     else:
>         return 1
> 
> a1 = 3
> b1 = 4
> a2 = 6
> b2 = 4
> 
> print(spam(a2, b2, a1, b1))
> 
> print(egg(a1, b1, a2, b2))
> 
> c = spam(a1, b2, a2, b1)
> 
> print(c)
> 
> c += egg(a1, b2, a2, b1)
> 
> print(c)
> ```

{{< details summary="**Answer of This Question**" >}}
The output of the given program will be:

```
0
1
0
1
```

Explanation:

1. The program defines two functions: `spam()` and `egg()`.

2. The `spam()` function takes four parameters (a1, b1, a2, b2) and returns 1 if a1 is equal to a2 and b1 is greater than b2. Otherwise, it returns 0.

3. The `egg()` function takes four parameters (a1, b1, a2, b2) and returns 0 if a1 is greater than a2 and b1 is equal to b2. Otherwise, it returns 1.

4. The program initializes four variables: a1 = 3, b1 = 4, a2 = 6, and b2 = 4.

5. The first `print()` statement calls the `spam()` function with arguments (a2, b2, a1, b1), which are (6, 4, 3, 4). Since a2 (6) is not equal to a1 (3), the function returns 0. Therefore, the first output is 0.

6. The second `print()` statement calls the `egg()` function with arguments (a1, b1, a2, b2), which are (3, 4, 6, 4). Since a1 (3) is not greater than a2 (6), the function returns 1. Therefore, the second output is 1.

7. The variable `c` is assigned the result of calling the `spam()` function with arguments (a1, b2, a2, b1), which are (3, 4, 6, 4). Since a1 (3) is not equal to a2 (6), the function returns 0. Therefore, `c` is assigned the value 0.

8. The third `print()` statement outputs the value of `c`, which is 0.

9. The line `c += egg(a1, b2, a2, b1)` is equivalent to `c = c + egg(a1, b2, a2, b1)`. It calls the `egg()` function with arguments (a1, b2, a2, b1), which are (3, 4, 6, 4). Since a1 (3) is not greater than a2 (6), the function returns 1. The returned value is added to the current value of `c`, which is 0. Therefore, `c` becomes 1.

10. The fourth `print()` statement outputs the updated value of `c`, which is 1.

In summary, the program outputs:
- 0 (result of `spam(a2, b2, a1, b1)`)
- 1 (result of `egg(a1, b1, a2, b2)`)
- 0 (value of `c` after calling `spam(a1, b2, a2, b1)`)
- 1 (value of `c` after adding the result of `egg(a1, b2, a2, b1)` to the previous value of `c`)
{{< /details >}}

### Copy Odd Lines

> Write a function called `copy_half` that takes the name of two files as arguments. The function should copy the first, third, fifth, etc. lines (i.e. odd lines only) from the first file to the second file. For example, if the file names are 'in.txt' and 'out.txt' and if 'in.txt' contains
> 
> ```text
> starting line
>   not this line
> middle line is here
>     skip this line too
>      I like this line
> ```
> 
> then after the call
> 
> ```python
> copy_half( 'in.txt', 'out.txt' )
> ```
> 
> the file 'out.txt' should contain
> 
> ```text
> starting line
> middle line is here
>     I like this line
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the solution to the problem:

```python
def copy_half(file1, file2):
    with open(file1, 'r') as input_file, open(file2, 'w') as output_file:
        lines = input_file.readlines()
        for i in range(0, len(lines), 2):
            output_file.write(lines[i])
```

Explanation:

1. The function `copy_half` takes two arguments: `file1` (the input file) and `file2` (the output file).

2. We open both files using the `with` statement, which ensures that the files are properly closed after we're done with them. We open `file1` in read mode ('r') and `file2` in write mode ('w').

3. We read all the lines from the input file using `readlines()` and store them in the `lines` list.

4. We start a `for` loop that iterates over the indices of `lines` with a step of 2 using `range(0, len(lines), 2)`. This ensures that we process only the odd-indexed lines (1st, 3rd, 5th, etc.).

5. Inside the loop, we write each odd-indexed line to the output file using `output_file.write(lines[i])`. This copies the line from the input file to the output file.

6. The loop continues until all the odd-indexed lines have been processed and written to the output file.

7. After the loop finishes, the `with` statement automatically closes both files.

So, when you call the function `copy_half('in.txt', 'out.txt')`, it will read the contents of 'in.txt', copy the odd-indexed lines (1st, 3rd, 5th, etc.), and write them to 'out.txt'. The resulting 'out.txt' file will contain only the odd lines from 'in.txt'.
{{< /details >}}

### Separate Positive and Negative Values

> Write a segment of code that reads integers from a file called `test2.txt` and stores the positive values in one list, the negative values in a second list, and skips blank lines and zeros. The order of the values in each list should match the order of the input. Each line of input will contain either spaces or spaces and an integer. For example, if `test2.txt` contains
> 
> ```python
>     11
> -3
> 
> 5
>   0
> ```
> 
> Then after your code, the list `P` should be `[ 11, 5 ]` and the list `N` should be `[ -3 ]`.

{{< details summary="**Answer of This Question**" >}}
Here's the code segment that reads integers from the file `test2.txt`, stores the positive values in a list `P`, stores the negative values in a list `N`, and skips blank lines and zeros:

```python
P = []
N = []

with open('test2.txt', 'r') as file:
    for line in file:
        line = line.strip()
        if line:
            num = int(line)
            if num > 0:
                P.append(num)
            elif num < 0:
                N.append(num)
```

Explanation:

1. We initialize two empty lists: `P` to store the positive values and `N` to store the negative values.

2. We open the file `test2.txt` in read mode using the `with` statement, which ensures that the file is properly closed after we're done with it.

3. We start a `for` loop that iterates over each line in the file using `for line in file:`.

4. For each line, we use `line.strip()` to remove any leading or trailing whitespace characters (including newline characters).

5. We check if the stripped line is not empty using `if line:`. This condition skips blank lines.

6. If the line is not empty, we convert it to an integer using `int(line)` and store it in the variable `num`.

7. We then check the value of `num`:
   - If `num` is greater than 0, we append it to the list `P` using `P.append(num)`.
   - If `num` is less than 0, we append it to the list `N` using `N.append(num)`.
   - If `num` is equal to 0, we skip it and move on to the next line.

8. The loop continues until all the lines in the file have been processed.

9. After the loop finishes, the `with` statement automatically closes the file.

So, after running this code segment, the list `P` will contain the positive values from the file `test2.txt` in the order they appeared, and the list `N` will contain the negative values in the order they appeared. Blank lines and zeros will be skipped.

For the given example, if `test2.txt` contains:

```
    11
-3

5
  0
```

Then the resulting lists will be:
- `P = [11, 5]`
- `N = [-3]`
{{< /details >}}

### Code Output 1

> Give the output of each of the following
> 
> (a)
> ```python
> i = 4
> L = [ 0, 12, 3, 5, 2, -1 ]
> while 0 <= i and i < len(L):
>     if L[i] < 0:
>         break
>     else:
>         i = L[i]
> print(i, L[i])
> ```
> 
> (b)
> ```python
> tough = 2
> for i in range(2):
>     s = 1
>     for j in range(i, tough):
>         s += tough
>     print(s)
>     print(tough)
>     tough = s
>     print(tough)
> ```

{{< details summary="**Answer of This Question**" >}}
(a) Output:
```
2 3
```

Explanation:
1. The variable `i` is initialized to 4.
2. The list `L` is defined as `[0, 12, 3, 5, 2, -1]`.
3. The `while` loop starts with the condition `0 <= i and i < len(L)`, which is true since `i` is 4 and the length of `L` is 6.
4. Inside the loop, the condition `L[i] < 0` is checked. Since `L[4]` is 2, which is not less than 0, the `else` block is executed.
5. In the `else` block, `i` is assigned the value of `L[i]`, which is `L[4] = 2`. So, `i` becomes 2.
6. The loop continues with the updated value of `i`, and the condition `0 <= i and i < len(L)` is still true.
7. The condition `L[i] < 0` is checked again. Since `L[2]` is 3, which is not less than 0, the `else` block is executed.
8. In the `else` block, `i` is assigned the value of `L[i]`, which is `L[2] = 3`. So, `i` becomes 3.
9. The loop continues with the updated value of `i`, and the condition `0 <= i and i < len(L)` is still true.
10. The condition `L[i] < 0` is checked again. Since `L[3]` is 5, which is not less than 0, the `else` block is executed.
11. In the `else` block, `i` is assigned the value of `L[i]`, which is `L[3] = 5`. So, `i` becomes 5.
12. The loop continues with the updated value of `i`, but the condition `0 <= i and i < len(L)` is now false since `i` is 5, which is not less than the length of `L`.
13. The loop terminates, and the values of `i` and `L[i]` are printed. At this point, `i` is 5 and `L[5]` is -1.
14. Therefore, the output is `2 3`.

(b) Output:
```
3
2
3
7
3
7
```

Explanation:
1. The variable `tough` is initialized to 2.
2. The outer `for` loop starts with `i` ranging from 0 to 1 (two iterations).
3. In the first iteration (`i = 0`):
   - `s` is initialized to 1.
   - The inner `for` loop starts with `j` ranging from 0 to 1 (two iterations).
   - In each iteration of the inner loop, `s` is incremented by `tough`, which is 2. So, `s` becomes 3.
   - After the inner loop, `s` is printed, which is 3.
   - `tough` is printed, which is 2.
   - `tough` is updated with the value of `s`, so `tough` becomes 3.
   - The updated value of `tough` is printed, which is 3.
4. In the second iteration (`i = 1`):
   - `s` is initialized to 1.
   - The inner `for` loop starts with `j` ranging from 1 to 2 (two iterations).
   - In each iteration of the inner loop, `s` is incremented by `tough`, which is now 3. So, `s` becomes 7.
   - After the inner loop, `s` is printed, which is 7.
   - `tough` is printed, which is 3.
   - `tough` is updated with the value of `s`, so `tough` becomes 7.
   - The updated value of `tough` is printed, which is 7.
5. The outer loop terminates, and the program ends.
6. Therefore, the output is:
   ```
   3
   2
   3
   7
   3
   7
   ```
{{< /details >}}

### Code Output 2

> Please show the output from the following code?
> 
> ```python
> def get_min(v):
>     v.sort()
>     return v[0]
> 
> def get_max(v):
>     x = max(v)
>     return x
> 
> v = [ 14, 19, 4, 5, 12, 8 ]
> if len(v) > 10 and get_min(v) > 6:
>     print("Hello")
>     print(v[0])
>     print(v[4])
> else:
>     print("So long")
>     print(v[0])
>     print(v[-1])
>     
>     if len(v) < 10 or get_max(v):
>         print(get_max(v))
>         print(v[0])
>         print(get_min(v))
>         print(v[0])
> ```

{{< details summary="**Answer of This Question**" >}}
The output from the given code will be:
```
So long
4
19
19
4
4
4
```

Explanation:
1. The list `v` is initialized with the values `[14, 19, 4, 5, 12, 8]`.
2. The `if` condition `len(v) > 10 and get_min(v) > 6` is evaluated:
   - `len(v)` is 6, which is not greater than 10.
   - The function `get_min(v)` is called, which sorts the list `v` in ascending order and returns the first element, which is 4. However, 4 is not greater than 6.
   - Since both conditions are not satisfied, the `else` block is executed.
3. Inside the `else` block:
   - The string "So long" is printed.
   - `v[0]`, which is 4, is printed.
   - `v[-1]`, which is 19, is printed.
4. The next `if` condition `len(v) < 10 or get_max(v)` is evaluated:
   - `len(v)` is 6, which is less than 10, so the condition is true.
   - The function `get_max(v)` is called, which returns the maximum value in the list `v`, which is 19. Since 19 is a truthy value, the condition is also true.
   - Since either of the conditions is true, the block inside the `if` statement is executed.
5. Inside the `if` block:
   - `get_max(v)`, which is 19, is printed.
   - `v[0]`, which is 4, is printed.
   - `get_min(v)`, which is 4 (since the list `v` is already sorted from the previous call to `get_min()`), is printed.
   - `v[0]`, which is 4, is printed again.
6. The program ends.

Therefore, the output will be:
```
So long
4
19
19
4
4
4
```
{{< /details >}}

### Elephant Steps

> Show the output from the following code:
> 
> ```python
> def elephant(height):
>     time_step = 1
>     steps = 0
>     while steps < height:
>         steps += time_step
>         steps -= time_step//3
>         time_step += 1
>     print("{}, {}".format(time_step, steps))
> 
> elephant(0)
> elephant(5)
> elephant(6)
> ```

{{< details summary="**Answer of This Question**" >}}
The output from the given code will be:
```
1, 0
5, 5
5, 6
```

Explanation:
1. The function `elephant(height)` is defined, which takes an integer `height` as input.
2. Inside the function:
   - The variable `time_step` is initialized to 1.
   - The variable `steps` is initialized to 0.
   - A `while` loop is started, which continues as long as `steps` is less than `height`.
   - Inside the loop:
     - `steps` is incremented by `time_step`.
     - `steps` is decremented by `time_step // 3` (integer division).
     - `time_step` is incremented by 1.
   - After the loop ends, the values of `time_step` and `steps` are printed using the `print()` function with the format string `"{}, {}"`.
3. The function `elephant()` is called with different arguments:
   - `elephant(0)`:
     - The loop is not executed since `steps` (0) is not less than `height` (0).
     - The values of `time_step` (1) and `steps` (0) are printed.
   - `elephant(5)`:
     - The loop iterates until `steps` becomes greater than or equal to `height` (5).
     - In each iteration:
       - `steps` is incremented by `time_step` (1, 2, 3, 4).
       - `steps` is decremented by `time_step // 3` (0, 0, 1, 1).
       - `time_step` is incremented by 1.
     - After the loop ends, the values of `time_step` (5) and `steps` (5) are printed.
   - `elephant(6)`:
     - The loop iterates until `steps` becomes greater than or equal to `height` (6).
     - The loop behaves similarly to the previous case, but since `height` is 6, the loop ends when `steps` becomes 6.
     - After the loop ends, the values of `time_step` (5) and `steps` (6) are printed.
4. The program ends.

Therefore, the output will be:
```
1, 0
5, 5
5, 6
```
{{< /details >}}

### Code Output 3

> Show the output of the following code. Make sure we can determine what is output and what is scratch work.
> 
> ```python
> def remove_something(z):
>     z.remove( z[z[0]] )
> 
> v = [ 1, 8, [12, 8], 'hello', 'car' ]
> x = 'salad'
> 
> if len(v[2]) >= 2:
>     if x > v[3]:
>         print( 'One')
>         if v[0] == 1:
>             print('Three')
>         else:
>             print('Two')
>     elif len(v) == 5:
>         print('Six')
>     else:
>         v.append('five')
>         print('Ten')
>         
> remove_something(v)
> print(v[1])
> print(v[2])
> v.append(x)
> print(len(v))
> ```

{{< details summary="**Answer of This Question**" >}}
Output:
```
Six
[12, 8]
hello
5
```

Explanation:
1. The function `remove_something(z)` is defined, which removes the element at index `z[0]` from the list `z`.
2. The list `v` is initialized with the values `[1, 8, [12, 8], 'hello', 'car']`.
3. The variable `x` is assigned the string value `'salad'`.
4. The `if` condition `len(v[2]) >= 2` is evaluated:
   - `v[2]` is `[12, 8]`, and its length is 2, so the condition is true.
5. The `if` condition `x > v[3]` is evaluated:
   - `x` is `'salad'` and `v[3]` is `'hello'`. Since `'salad'` is lexicographically greater than `'hello'`, the condition is false.
6. The `elif` condition `len(v) == 5` is evaluated:
   - `len(v)` is 5, so the condition is true.
   - The string `'Six'` is printed.
7. The function `remove_something(v)` is called with `v` as the argument:
   - Inside the function, `z[0]` is 1, so `z[z[0]]` is `z[1]`, which is 8.
   - The element 8 is removed from the list `v`.
8. `v[1]` is printed, which is now `[12, 8]` (since 8 was removed from the list).
9. `v[2]` is printed, which is now `'hello'` (since the element at index 1 was removed).
10. The string `x` (`'salad'`) is appended to the list `v`.
11. `len(v)` is printed, which is now 5 (since one element was removed and one element was added).
12. The program ends.

Therefore, the output will be:
```
Six
[12, 8]
hello
5
```
{{< /details >}}

### Print Grid

> You are given a list of lists represented as an NxN grid in which each list corresponds to one row of the grid. For example, a 4x4 grid is given by:
> 
> ```python
> [[1,2,3,4],[4,3,2,1],[2,1,4,2],[2,1,4,5]]
> ```
> 
> Write a piece of code to print the grid in the following format with a vertical and horizontal line right in the middle:
> 
> ```text
> 1 2 | 3 4
> 4 3 | 2 1
> ----|----
> 2 1 | 4 2
> 2 1 | 4 5
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the Python code to print the grid in the desired format:

```python
def print_grid(grid):
    n = len(grid)
    mid = n // 2

    for i in range(n):
        row = grid[i]
        for j in range(n):
            if j == mid:
                print("|", end=" ")
            print(row[j], end=" ")
        print()
        if i == mid - 1:
            print("-" * (n * 2 + 1))

# Example usage
grid = [[1,2,3,4],[4,3,2,1],[2,1,4,2],[2,1,4,5]]
print_grid(grid)
```

Explanation:

1. The function `print_grid` takes a list of lists `grid` as input, representing the NxN grid.

2. We calculate the length of the grid `n` and the middle index `mid` by dividing `n` by 2 using integer division (`//`).

3. We start a loop that iterates over each row of the grid using the index `i`.

4. For each row, we retrieve the current row `row` from the grid using `grid[i]`.

5. We start another loop that iterates over each element of the current row using the index `j`.

6. Inside the inner loop, we check if the current column index `j` is equal to the middle index `mid`. If it is, we print a vertical bar (`|`) followed by a space.

7. We print the current element `row[j]` followed by a space.

8. After printing all the elements of the current row, we move to the next line using `print()`.

9. After printing each row, we check if the current row index `i` is equal to `mid - 1`. If it is, we print a horizontal line (`-`) of length `n * 2 + 1` (the number of elements in each row multiplied by 2 plus 1 for the vertical bar).

10. Finally, we provide an example usage of the `print_grid` function by creating a 4x4 grid and calling the function with the grid as an argument.

The output will be:
```
1 2 | 3 4 
4 3 | 2 1 
----|----
2 1 | 4 2 
2 1 | 4 5 
```

This code prints the grid in the desired format, with a vertical bar (`|`) in the middle of each row and a horizontal line (`-`) in the middle of the grid.
{{< /details >}}

### Sum and Count Numbers

> Write a piece of code that repeatedly asks the user for numbers using input until the user enters 'stop'. Then, the program reports the sum of the values entered by the user and the total number of values strictly greater than zero. You can assume that the user enters a valid number until she enters stop.
> 
> An example run of this code is given below.
> 
> ```text
> Enter a value ==> 1.2
> Enter a value ==> 0
> Enter a value ==> 2
> Enter a value ==> -1
> Enter a value ==> stop
> Sum: 2.2
> Values > 0: 2
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the Python code that repeatedly asks the user for numbers until 'stop' is entered, and then reports the sum of the values and the count of values strictly greater than zero:

```python
def sum_and_count_numbers():
    total_sum = 0
    count_positive = 0

    while True:
        user_input = input("Enter a value ==> ")
        if user_input == 'stop':
            break

        try:
            number = float(user_input)
            total_sum += number
            if number > 0:
                count_positive += 1
        except ValueError:
            print("Invalid input. Please enter a valid number.")

    print("Sum:", total_sum)
    print("Values > 0:", count_positive)

# Example usage
sum_and_count_numbers()
```

Explanation:

1. The function `sum_and_count_numbers` is defined to perform the desired task.

2. We initialize two variables: `total_sum` to keep track of the sum of all the numbers entered by the user, and `count_positive` to count the number of values strictly greater than zero.

3. We start an infinite loop using `while True` to repeatedly ask the user for input.

4. Inside the loop, we prompt the user to enter a value using `input()` and store it in the `user_input` variable.

5. We check if the `user_input` is equal to 'stop'. If it is, we break out of the loop using the `break` statement, indicating that the user wants to stop entering values.

6. If the `user_input` is not 'stop', we attempt to convert it to a float using `float()` and store it in the `number` variable. We use a `try-except` block to handle any potential `ValueError` that may occur if the user enters an invalid input.

7. If the conversion to float is successful, we add the `number` to the `total_sum` using the `+=` operator.

8. We then check if the `number` is strictly greater than zero using the condition `number > 0`. If it is, we increment the `count_positive` variable by 1.

9. If a `ValueError` occurs during the conversion to float, we catch the exception and print an error message to inform the user to enter a valid number.

10. After the loop ends (when the user enters 'stop'), we print the `total_sum` and `count_positive` values using `print()`.

11. Finally, we provide an example usage of the `sum_and_count_numbers` function by calling it.

The code will repeatedly prompt the user to enter values until 'stop' is entered. It will calculate the sum of all the entered values and count the number of values strictly greater than zero. The output will be similar to the example run provided in the question.
{{< /details >}}

### Remove Value from List

> Write a function `remove_val(l,val)` that removes all copies of `val` from list `l`.
> 
> Suppose you are given a variable `x` containing numbers as shown below:
> 
> ```python
> x = [1, 4, 2, 1, 2, 4, 4, 2, 5, 5, 2]
> ```
> 
> Then, your function should work as follows:
> 
> ```python
> >>> remove_val(x,4)
> >>> x
> [1, 2, 1, 2, 2, 5, 5, 2]
> ```
> 
> Note: if your function returns a new list with this content instead of modifying it as given, you will lose points. Also, be careful with this one. The code:
> 
> (a)
> ```python
> def remove_val(l,val):
>     for item in l:
>         if item == val:
>             l.remove(val)
> ```
> 
> and
> 
> (b)
> ```python
> def remove_val(l,val):
>     for index in range(len(l)):
>         if l[index] == val:
>             l.pop(index)
> ```
> 
> will not work. Can you explain why? Try writing (a) using a while loop and see if that makes it clearer. For (b) try running it in the debugger.

{{< details summary="**Answer of This Question**" >}}
Here's the correct implementation of the `remove_val` function that removes all occurrences of `val` from the list `l`:

```python
def remove_val(l, val):
    while val in l:
        l.remove(val)
```

Explanation:
- The function `remove_val` takes two parameters: `l` (the list) and `val` (the value to be removed).
- We use a `while` loop to repeatedly check if `val` is present in the list `l` using the `in` operator.
- If `val` is found in the list, we remove it using the `list.remove()` method.
- The loop continues until all occurrences of `val` are removed from the list.

Now, let's discuss why the two given implementations (a) and (b) do not work correctly:

(a) Using a `for` loop:
```python
def remove_val(l, val):
    for item in l:
        if item == val:
            l.remove(val)
```
Explanation:
- The problem with this implementation is that it modifies the list while iterating over it using a `for` loop.
- When an element is removed from the list, the indices of the subsequent elements shift, causing the loop to skip some elements.
- As a result, not all occurrences of `val` are removed from the list.

(b) Using `range()` and `pop()`:
```python
def remove_val(l, val):
    for index in range(len(l)):
        if l[index] == val:
            l.pop(index)
```
Explanation:
- This implementation also suffers from the same issue as (a).
- When an element is removed using `pop()`, the indices of the subsequent elements shift.
- However, the loop continues to the next index, potentially skipping elements that match `val`.
- Consequently, not all occurrences of `val` are removed from the list.

To understand the issue more clearly, you can run the code in a debugger and step through it to see how the indices change after each removal.

The correct approach is to use a `while` loop as shown in the first implementation. It repeatedly checks for the presence of `val` in the list and removes it until all occurrences are eliminated.

Example usage:
```python
x = [1, 4, 2, 1, 2, 4, 4, 2, 5, 5, 2]
remove_val(x, 4)
print(x)  # Output: [1, 2, 1, 2, 2, 5, 5, 2]
```

The function modifies the original list `x` by removing all occurrences of the value `4`.
{{< /details >}}

### Compare Athlete Scores

> Suppose you are given the scores of two athletes in various competitions, provided as two separate lists. Assume there are unknown number of competitions numbered 1,2,3, etc. and the length of the two lists is the same.
> 
> ```python
> a1 = [11,8,11,9]
> a2 = [11,9,8,12]
> ```
> 
> For example according this to list, both athletes got a score of 11 in competition 1. Print the index of all the competitions in which `a2` did better. For example, for the above lists, we would print:
> 
> ```python
> a2 is better in 2 4
> ```
> 
> If there is no value in which `a2` is better, then you should print:
> 
> ```python
> a2 is never better
> ```

{{< details summary="**Answer of This Question**" >}}
Here's a Python script that compares the scores of two athletes in various competitions and prints the index of the competitions in which `a2` did better:

```python
def compare_scores(a1, a2):
    better_indices = []
    for i in range(len(a1)):
        if a2[i] > a1[i]:
            better_indices.append(i + 1)

    if better_indices:
        print("a2 is better in", ' '.join(map(str, better_indices)))
    else:
        print("a2 is never better")

# Example usage
a1 = [11, 8, 11, 9]
a2 = [11, 9, 8, 12]
compare_scores(a1, a2)
```

Explanation:

1. The function `compare_scores` takes two lists `a1` and `a2` as parameters, representing the scores of two athletes in various competitions.

2. We initialize an empty list called `better_indices` to store the indices of the competitions in which `a2` did better.

3. We start a loop that iterates over the indices of the scores using `range(len(a1))`. Since both lists are assumed to have the same length, we can use the length of either list.

4. Inside the loop, we compare the scores of `a2` and `a1` at each index using the condition `a2[i] > a1[i]`. If `a2` has a higher score at the current index, we append the index plus 1 to the `better_indices` list. We add 1 to the index because the competitions are numbered starting from 1.

5. After the loop ends, we check if the `better_indices` list is not empty using an `if` statement.

6. If `better_indices` is not empty, it means `a2` did better in at least one competition. We print "a2 is better in" followed by the indices of the competitions where `a2` did better. We use the `join()` method to concatenate the indices into a string, separated by spaces. The `map(str, better_indices)` is used to convert the indices to strings before joining them.

7. If `better_indices` is empty, it means `a2` did not do better in any competition. In this case, we print "a2 is never better".

8. Finally, we provide an example usage of the `compare_scores` function by calling it with the given lists `a1` and `a2`.

The output for the example lists will be:
```
a2 is better in 2 4
```

This indicates that `a2` did better in competitions 2 and 4.

If `a2` never did better in any competition, the output will be:
```
a2 is never better
```

This script compares the scores of two athletes and prints the indices of the competitions in which `a2` did better, or "a2 is never better" if `a2` did not do better in any competition.
{{< /details >}}

### List Slicing Output

> What is the output from the following code:
> 
> ```python
> >>> L1 = ['cat', 'dog', 'hawk', 'tiger', 'parrot']
> >>> print(L1[1:-1])
> >>> print(L1[1:-2])
> >>> print(L1[1:-4])
> >>> print(L1[1:0])
> >>> print(L1[1:10])
> >>> print(L1[::-1])
> >>> print(L1[1:4:2])
> >>> print(L1[::-2])
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the output from the given code:

```python
['dog', 'hawk', 'tiger']
['dog', 'hawk']
[]
[]
['dog', 'hawk', 'tiger', 'parrot']
['parrot', 'tiger', 'hawk', 'dog', 'cat']
['dog', 'tiger']
['parrot', 'hawk', 'cat']
```

Explanation:

1. `print(L1[1:-1])`:
   - This slices the list `L1` from index 1 (inclusive) to the second-to-last index (exclusive).
   - The output is `['dog', 'hawk', 'tiger']`.

2. `print(L1[1:-2])`:
   - This slices the list `L1` from index 1 (inclusive) to the third-to-last index (exclusive).
   - The output is `['dog', 'hawk']`.

3. `print(L1[1:-4])`:
   - This slices the list `L1` from index 1 (inclusive) to the fifth-to-last index (exclusive).
   - Since there are only 5 elements in the list, this results in an empty slice.
   - The output is `[]`.

4. `print(L1[1:0])`:
   - This slices the list `L1` from index 1 (inclusive) to index 0 (exclusive).
   - Since the ending index is less than the starting index, this results in an empty slice.
   - The output is `[]`.

5. `print(L1[1:10])`:
   - This slices the list `L1` from index 1 (inclusive) to index 10 (exclusive).
   - Since the list has only 5 elements, the ending index goes beyond the list's length, but it doesn't cause an error. It simply includes all elements from index 1 to the end of the list.
   - The output is `['dog', 'hawk', 'tiger', 'parrot']`.

6. `print(L1[::-1])`:
   - This slices the list `L1` with a step of -1, which reverses the list.
   - The output is `['parrot', 'tiger', 'hawk', 'dog', 'cat']`.

7. `print(L1[1:4:2])`:
   - This slices the list `L1` from index 1 (inclusive) to index 4 (exclusive) with a step of 2.
   - It includes every second element within the specified range.
   - The output is `['dog', 'tiger']`.

8. `print(L1[::-2])`:
   - This slices the list `L1` with a step of -2, which reverses the list and includes every second element.
   - The output is `['parrot', 'hawk', 'cat']`.

These examples demonstrate different ways of slicing a list in Python using start index, end index, and step size.
{{< /details >}}

### Code Output 4

> What is the output of the following programs:
> 
> #### Part a
> 
> ```python
> a = 25
> b = 11
> while True:
>     print(a, b)
>     if a <= 0 or b <= 0:
>         break
>     if a > b:
>         a = a - b
>     else:
>         b = b - a
>     b -= 1
>     a += 1
> ```
> 
> #### Part b
> 
> ```python
> mylist = [10, -5, 4, 8, 1000, -1, -120, 18, 5.2]
> for item in mylist:
>     if item < 0:
>         continue
>     print(item)
> ```
> 
> #### Part c
> 
> ```python
> def spam(l,s):
>     m = len(s)//2
>     s1 = s[:m]
>     s2 = s[m:]
>     if l.count(s1) == 0:
>         l.append(s1)
>     if l.count(s2) == 0:
>         l.append(s2)
> 
> l = ['ab','cd','de','fg']
> s1 = 'abcde'
> s2 = 'fghi'
> spam(l,s1)
> print(s1)
> l = spam(l,s2)
> print(s2)
> print(l)
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the output of each program:

#### Part a

```
25 11
15 10
6 9
6 8
7 7
1 6
8 5
4 4
1 3
5 2
4 1
4 0
```

Explanation:
- The program starts with `a = 25` and `b = 11`.
- It enters an infinite loop and prints the values of `a` and `b` in each iteration.
- Inside the loop, it checks if either `a` or `b` becomes less than or equal to 0. If so, it breaks out of the loop.
- If `a` is greater than `b`, it subtracts `b` from `a`. Otherwise, it subtracts `a` from `b`.
- After the subtraction, it decrements `b` by 1 and increments `a` by 1.
- The loop continues until the break condition is met, and the program terminates.

#### Part b

```
10
4
8
1000
18
5.2
```

Explanation:
- The program iterates over the elements in `mylist`.
- For each element, it checks if the element is less than 0 using the condition `if item < 0`.
- If the element is less than 0, it skips that element using the `continue` statement and moves to the next iteration.
- If the element is greater than or equal to 0, it prints the element.
- The program continues until all elements in `mylist` have been processed.

#### Part c

```
abcde
fghi
['ab', 'cd', 'de', 'fg', 'ab', 'cd', 'fg', 'hi']
```

Explanation:
- The program defines a function `spam` that takes a list `l` and a string `s` as parameters.
- Inside the function, it calculates the middle index `m` of the string `s` using integer division.
- It splits the string `s` into two halves: `s1` (from the start to the middle index) and `s2` (from the middle index to the end).
- It checks if `s1` is not present in the list `l` using `l.count(s1) == 0`. If so, it appends `s1` to the list `l`.
- Similarly, it checks if `s2` is not present in the list `l` using `l.count(s2) == 0`. If so, it appends `s2` to the list `l`.
- The program initializes a list `l` with `['ab', 'cd', 'de', 'fg']` and two strings `s1` and `s2`.
- It calls the `spam` function with `l` and `s1` as arguments.
- It prints the value of `s1`, which remains unchanged.
- It calls the `spam` function again with `l` and `s2` as arguments, but the return value is not assigned to any variable.
- It prints the value of `s2`, which remains unchanged.
- Finally, it prints the updated list `l`, which includes the original elements and the split halves of `s1` and `s2` that were not already present in the list.

These programs demonstrate different concepts such as loops, conditionals, list manipulation, and function calls in Python.
{{< /details >}}

### More "What Is the Output?" Questions

> ```python
> print(4**3)
> print(2**2**3)
> ----------------
> for i in range(2,10,2):
>     print(i)
> ----------------
> j=2
> while(j<10):
>     print(j)
>     j=j+2
> L=[1,2,3,(7,8,'truck')]
> L.insert(-1,L.pop())
> print(L)
> ----------------
> pokeballs = ["net", "ultra", "dusk", "great", "great", "great"]
> while(True and pokeballs.pop() == "great"):
>     print(pokeballs)
>     print(pokeballs[-1] == "great")
> ----------------
> list1 = [6,8,10]
> list2 = [[3,5,7], list1, list(list1)]
> list1.append(list2[0].pop())
> print(list2)
> ----------------
> j=11
> while(True):
>     print('-',end='')
>     i=0
>     if i >= 5:
>         break
>     elif j <= 4:
>         break
>     j = j - 1
>     if j%2 == 1:
>         continue
>     print('*',end='')
>     i = i + 2
> ----------------
> a = "and".join(list("1234"))
> b = a.split('and')
> c = b
> b.append('5')
> c.append('6')
> print(a)
> print(b)
> print(c)
> c = b[:]
> b.append('7')
> c.append('8')
> print(b)
> print(c)
> ----------------
> lst = ['dog', 'cat', 'chat']
> print('dog' in lst and 'hat' in lst[2])
> ----------------
> print(not True or True and False == False)
> ----------------
> symbols = ['5', 'p', 'P', '100', '!', 'pika', 'Pika', 'pIka', '44']
> print(sorted(symbols))
> print(symbols[::].sort())
> print(symbols)
> print(symbols.sort())
> print(symbols)
> print(symbols[::-1])
> ----------------
> def someFunc(myList, myTuple):
>     myTuple = (4,3,2,1)
>     for pikachu in myList:
>         myList[pikachu-1] = str(pikachu) + "pika"
>     return True
> aList = [1, 2, 3, 4]
> aTuple = (1, 2, 3, 4)
> if someFunc(aList, aTuple):
>     print(aTuple)
>     print(aList)
> ----------------
> waterTypes = ["Oshawott", "Froakie", "Squirtle", "Kyogre"]
> print(waterTypes[0:3:2])
> print(waterTypes[1::2])
> print(waterTypes[-1:0:-2])
> print(waterTypes[-2::-2])
> wT2 = waterTypes[0:4:1].append("Magikarp")
> print(wT2)
> wT2 = waterTypes[0:4:1]
> print(wT2)
> print(wT2[:1] + wT2[-3:3] + wT2[-2:-3] + wT2[3:] + ["Magikarp"])
> ```

{{< details summary="**Answer of This Question**" >}}
Here's the output for each code snippet:

```
64
256
----------------
2
4
6
8
----------------
2
4
6
8
[1, 2, 3, (7, 8, 'truck')]
----------------
['net', 'ultra', 'dusk', 'great', 'great']
False
['net', 'ultra', 'dusk', 'great']
False
['net', 'ultra', 'dusk']
False
----------------
[[3, 5], [6, 8, 10, 7], [6, 8, 10]]
----------------
-*-*-*-*-*-
----------------
1and2and3and4
['1', '2', '3', '4', '5', '6']
['1', '2', '3', '4', '5', '6']
['1', '2', '3', '4', '5', '6', '7']
['1', '2', '3', '4', '5', '6', '8']
----------------
True
----------------
True
----------------
['!', '100', '44', '5', 'P', 'Pika', 'p', 'pIka', 'pika']
None
['!', '100', '44', '5', 'P', 'Pika', 'p', 'pIka', 'pika']
None
['!', '100', '44', '5', 'P', 'Pika', 'p', 'pIka', 'pika']
['pika', 'pIka', 'p', 'Pika', 'P', '5', '44', '100', '!']
----------------
(1, 2, 3, 4)
['1pika', '2pika', '3pika', '4pika']
----------------
['Oshawott', 'Squirtle']
['Froakie', 'Kyogre']
['Kyogre', 'Squirtle']
['Squirtle', 'Oshawott']
None
['Oshawott', 'Froakie', 'Squirtle', 'Kyogre']
['Oshawott', 'Squirtle', 'Kyogre', 'Kyogre', 'Magikarp']
```

Explanation for each code snippet:

1. `4**3` evaluates to 64, and `2**2**3` evaluates to 256 due to the right-to-left associativity of the exponentiation operator (`**`).

2. The `for` loop prints the even numbers from 2 to 8 (inclusive) with a step of 2.

3. The `while` loop prints the even numbers from 2 to 8 (inclusive) with a step of 2.

4. The last element of the list `L` is popped using `L.pop()` and inserted at the second-to-last position using `L.insert(-1, ...)`. The resulting list is printed.

5. The `while` loop iterates until the last element of `pokeballs` is not equal to "great". In each iteration, it prints the current state of `pokeballs` and the result of the comparison `pokeballs[-1] == "great"`.

6. The last element of `list2[0]` is popped and appended to `list1`. The resulting `list2` is printed.

7. The `while` loop prints a pattern of dashes and asterisks based on the conditions and iterations.

8. The string "1234" is split into a list, joined with "and", split again, and the resulting list is modified by appending elements. The variables `a`, `b`, and `c` are printed at different stages.

9. The expression `'dog' in lst and 'hat' in lst[2]` evaluates to `True` because both conditions are true.

10. The expression `not True or True and False == False` evaluates to `True` due to the order of operations and the truthiness of the operands.

11. The list `symbols` is sorted in ascending order using `sorted()`, and the result is printed. The `sort()` method is called on `symbols` and its slices, modifying the original list. The reversed list is printed using slicing with a step of -1.

12. The function `someFunc` modifies the elements of `aList` by appending "pika" to each element. The tuple `aTuple` remains unchanged. The modified `aList` and the original `aTuple` are printed.

13. Various slicing operations are performed on the `waterTypes` list, and the results are printed. The `append()` method is called on a slice of `waterTypes`, but the returned value is `None`. The last line concatenates slices of `wT2` and a new element "Magikarp" to create a new list.
{{< /details >}}

### Remove Elements from List 1

> And a final, really hard one ... Ask about it and we can go over why in review.
> 
> ```python
> r = 10*[1]
> for i in range(len(r)):
>     r.remove(1)
> print(r)
> L = 10*[1]
> for l in L:
>     L.remove(l)
> print(L)
> ```

{{< details summary="**Answer of This Question**" >}}
The code snippet you provided demonstrates two different ways of attempting to remove elements from a list, but both approaches have issues. Let's analyze each case:

Case 1:
```python
r = 10*[1]
for i in range(len(r)):
    r.remove(1)
print(r)
```

Explanation:
- The list `r` is initialized with 10 occurrences of the value `1`.
- The `for` loop iterates over the indices of `r` using `range(len(r))`.
- In each iteration, the first occurrence of `1` is removed from `r` using `r.remove(1)`.
- However, as elements are removed from the list, the indices of the remaining elements shift.
- The loop continues to the next index, potentially skipping elements.
- As a result, only the first 5 occurrences of `1` are removed, and the final list `r` contains `[1, 1, 1, 1, 1]`.

Case 2:
```python
L = 10*[1]
for l in L:
    L.remove(l)
print(L)
```

Explanation:
- The list `L` is initialized with 10 occurrences of the value `1`.
- The `for` loop iterates over the elements of `L` directly.
- In each iteration, the first occurrence of the current element `l` is removed from `L` using `L.remove(l)`.
- However, modifying the list while iterating over it using a `for` loop leads to unexpected behavior.
- As elements are removed, the indices of the subsequent elements shift, causing the loop to skip some elements.
- Consequently, only alternate occurrences of `1` are removed, resulting in the final list `L` containing `[1, 1, 1, 1, 1]`.

In both cases, the desired outcome of removing all occurrences of `1` from the list is not achieved.

To correctly remove all occurrences of an element from a list, you can use a `while` loop as shown in the previous answer:

```python
def remove_val(l, val):
    while val in l:
        l.remove(val)
```

This approach repeatedly checks for the presence of `val` in the list `l` and removes it until all occurrences are eliminated.

Example usage:
```python
r = 10*[1]
remove_val(r, 1)
print(r)  # Output: []

L = 10*[1]
remove_val(L, 1)
print(L)  # Output: []
```

In both cases, all occurrences of `1` are successfully removed from the lists `r` and `L`, resulting in empty lists.

It's important to be cautious when modifying a list while iterating over it, as it can lead to unexpected behavior. Using a `while` loop or creating a new list with the desired elements are safer approaches.
{{< /details >}}

### Remove Elements from List 2

> Okay not really a "What's the Output" but similar. See if you can explain this one:
> 
> ```python
> r = 10*[1]
> for i in range(len(r)):
>     r.remove(r[i])
> print(r)
> ```

{{< details summary="**Answer of This Question**" >}}
The code snippet you provided attempts to remove elements from the list `r` using a `for` loop and the `remove()` method, but it leads to unexpected behavior. Let's analyze it step by step:

```python
r = 10*[1]
for i in range(len(r)):
    r.remove(r[i])
print(r)
```

Explanation:
1. The list `r` is initialized with 10 occurrences of the value `1`.
2. The `for` loop iterates over the indices of `r` using `range(len(r))`.
3. In each iteration, the element at index `i` is removed from `r` using `r.remove(r[i])`.
4. However, as elements are removed from the list, the indices of the remaining elements shift.
5. The loop continues to the next index, which now corresponds to a different element than originally intended.

Let's trace the execution of the code:
- Initially, `r` is `[1, 1, 1, 1, 1, 1, 1, 1, 1, 1]`.
- In the first iteration (`i = 0`), `r[0]` is `1`, so `1` is removed from `r`. After removal, `r` becomes `[1, 1, 1, 1, 1, 1, 1, 1, 1]`.
- In the second iteration (`i = 1`), `r[1]` is now the second `1` in the updated list. It is removed, and `r` becomes `[1, 1, 1, 1, 1, 1, 1, 1]`.
- In the third iteration (`i = 2`), `r[2]` is now the third `1` in the updated list. It is removed, and `r` becomes `[1, 1, 1, 1, 1, 1, 1]`.
- The loop continues, removing every other element from the list.

After the loop finishes, the resulting list `r` will be `[1, 1, 1, 1, 1]`.

The issue with this code is that it modifies the list while iterating over it using indices. As elements are removed, the indices of the subsequent elements shift, causing the loop to skip some elements and leading to unexpected behavior.

To correctly remove all occurrences of an element from a list, you can use a `while` loop as shown in the previous answers:

```python
def remove_val(l, val):
    while val in l:
        l.remove(val)
```

This approach repeatedly checks for the presence of `val` in the list `l` and removes it until all occurrences are eliminated.

Example usage:
```python
r = 10*[1]
remove_val(r, 1)
print(r)  # Output: []
```

In this case, all occurrences of `1` are successfully removed from the list `r`, resulting in an empty list.

It's important to be cautious when modifying a list while iterating over it, as it can lead to unexpected behavior. Using a `while` loop or creating a new list with the desired elements are safer approaches.
{{< /details >}}