List Comprehension r/learnpython

# < ==========================================
# < Functions and Methods
# < ==========================================

def append(_list, item) -> None:
    """Method to add an item to a list"""
    # Built-in code goes here
    return None

def double(number) -> int:
    """Function to double a number"""
    return number * 2

# < ==========================================
# < Test One
# < ==========================================

output = [double(i) for i in range(1, 11)]
print(output)
# output = [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
# The left side of double(i) for i in range(1, 11) is evaluated each time
# Each item in the output list is evaluated to be the return of double(i), which returns an integer

# < ==========================================
# < Test Two
# < ==========================================

squares = []
print(f"Squares list before running [squares.append(i * i) for i in range(1, 11)]: {squares}")
# Squares list before running [squares.append(i * i) for i in range(1, 11)]: []

output = [squares.append(i * i) for i in range(1, 11)]
print(output)
# output = [None, None, None, None, None, None, None, None, None, None]
# The left side of squares.append(i * i) for i in range(1, 11) is evaluated each time
# Each item in the output list is evaluated to be the return of squares.append(i * i), which returns None

print(f"Squares list after running [squares.append(i * i) for i in range(1, 11)]: {squares}")
# Squares list after running [squares.append(i * i) for i in range(1, 11)]: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]