x = [2]

def square_numbers_1(numbers):
    for number in numbers:           # fails; number is copy of numbers[i]
        number = number*number
        x[0] = 3

def square_numbers_2(numbers):
    for i in range(len(numbers)):    # OK; modifies list in place
        numbers[i] = numbers[i]**2

def square_numbers_3(numbers):       # often best; returns new list
    new_list = []
    for number in numbers:
        new_list.append(number**2)
    return new_list


ints = [5, 8, 10]
print "before: ints = ", ints

square_numbers_1(ints)
print "1: ints = ", ints

square_numbers_2(ints)
print "2: ints = ", ints

new_list = square_numbers_3(ints)
print "3: ints = ", new_list


def square_number(x):
    x = x**2

a = 3
square_number(a)