Numbers passed as command line arguments in python not interpreted as integers

Question

I am familiar with C, and have started experimenting in python. My question is regarding the sys.argv command. I've read it is used for a command line interpreter, but when trying to execute a simple program I don't get the results I expect.

Code:

import sys  a = sys.argv[1] b = sys.argv[2]  print a, b  print a+b 

Input:

python mySum.py 100 200 

Output:

100 200 100200 

When I add the two arguments they are concatenated instead of the two values being added together. It seems that the values are being taken as strings.

How can I interpret them as numerics?

Answer 1

You can convert the arguments to integers using int()

import sys  a = int(sys.argv[1])  b = int(sys.argv[2])  print a, b  print a+b 

input: python mySum.py 100 200

output:

100 200 300 

Answer 2

You also should validate the user input:

import sys  def is_intstring(s):     try:         int(s)         return True     except ValueError:         return False  for arg in sys.argv[1:]:     if not is_intstring(arg):         sys.exit("All arguments must be integers. Exit.")  numbers = [int(arg) for arg in sys.argv[1:]] sum = sum(numbers)  print "The sum of arguments is %s" % sum