def remove_0(l):
    ''' Remove all instances of 0 from list l.'''

    while l.count(0) > 0:
        # Use a method that changes the list, if we want
        #  to affect the list we called the function with.
        l.remove(0)

def main():
    nums = [0, 1, 2, 30, 2, 0, 1, 0, 0, 1]
    print(nums)
    remove_0(nums) 
    print (nums,"should be",[1, 2, 30, 2, 1, 1] )
    nums = []
    remove_0(nums)
    print(nums,"should be the empty list")

main()