Problem C
Remove Odds

Write two functions for removing odd numbers from integer lists:

• extract_evens(int_list):
  Returns a new list with only even integers from int_list, without modifying int_list.

• remove_odds(int_list):
  Removes odd integers from int_list, thus modifying int_list.

Hint: Functions have the ability to modify mutable objects in the calling program. Lists are mutable objects.

The main file, which handles input and output, is already provided. - Please only submit your function definitions, without any code outside the functions!

Input

Each of the functions should accept one list $l$ as a parameter. You may assume the elements of the list $l$ will be integers.

In the samples below, the input consists of one line containing a sequence $x = (x_1, \dots , x_n)$ of $n$ numbers separated by a space. The autograder will handle reading the input, splitting it, converting to integers and passing the resulting list as an argument to the functions.

In the tests, $x$ will always satisfy $1 \le n \le 1\, 000$ and $1 \le x_i < 100$ for all $i$ with $1 \le i \le n$.

Output

The function extract_evens() should return a new list $e$ containing all the even numbers appearing in $l$, in the same order as they appear in $l$, and no other numbers. After the function is called, the original list $l$ should remain unchanged.

The function remove_odds() should return nothing (just None), but should modify the given list $l$, so that after the function is called, the list will have changed to a modified list $l'$ containing all the even numbers appearing in $l$, in the same order as they appear in $l$, and no other numbers.

In each test case, the autograder will call both of the functions with the given list as a parameter, in sequence, and will verify the results as well as the effects on the given list, and print the following four lines to the output, as seen in the samples below:

• “Original list before calling functions: {$l$}”

• “Resulting list after extracting evens: {$e$}”

• “Original list after extracting evens and before removing odds: {$l$}”

• “Original list after removing odds: {$l'$}”

1 1 2 3 4 5

Original list before calling functions: [1, 1, 2, 3, 4, 5]
Resulting list after extracting evens: [2, 4]
Original list after extracting evens and before removing odds: [1, 1, 2, 3, 4, 5]
Original list after removing odds: [2, 4]

10 7 7 7 7 1 10 9 9

Original list before calling functions: [10, 7, 7, 7, 7, 1, 10, 9, 9]
Resulting list after extracting evens: [10, 10]
Original list after extracting evens and before removing odds: [10, 7, 7, 7, 7, 1, 10, 9, 9]
Original list after removing odds: [10, 10]

1 1 2 3 4 5 6 7 8 9 10

Original list before calling functions: [1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Resulting list after extracting evens: [2, 4, 6, 8, 10]
Original list after extracting evens and before removing odds: [1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Original list after removing odds: [2, 4, 6, 8, 10]

9 1 3 3 52 7

Original list before calling functions: [9, 1, 3, 3, 52, 7]
Resulting list after extracting evens: [52]
Original list after extracting evens and before removing odds: [9, 1, 3, 3, 52, 7]
Original list after removing odds: [52]