"""calc.py: A simple Python calculator."""
import sys

def add_all(nums):
    return sum (nums)

def multiply_all(nums):
    return reduce(lambda a, b: a * b, nums)

if __name__ == '__main__':
    command = sys.argv[1]
    nums = map(float, sys.argv[2:])
    if command == 'add':
        print (add_all(nums))
    elif command == 'multiply':
        print(multiply_all(nums))

"""calc.py: A simple Python calculator."""
import sys

def add_all(nums):
    return sum (nums)

def multiply_all(nums):
    return reduce(lambda a, b: a * b, nums)

if __name__ == '__main__':
    command = sys.argv[1]
    nums = map(float, sys.argv[2:])
    if command == 'add':
        print (add_all(nums))
    elif command == 'multiply':
        print(multiply_all(nums))
    else:
        usage = "calc.py [add|multiply] NUM1 [NUM2 [NUM3 [...]]]"
        print(usage)

Add usage message