Argv - String into Integer

python argv
Andrew Blanchette picture Andrew Blanchette · Jun 29, 2013 · Viewed 38k times · Source

I'm pretty new at python and I've been playing with argv. I wrote this simple program here and getting an error that says :

TypeError: %d format: a number is required, not str

from sys import argv

file_name, num1, num2 = argv
int(argv[1])
int(argv[2])
def addfunc(num1, num2):
    print "This function adds %d and %d" % (num1, num2)
    return num1 + num2

addsum = addfunc(num1, num2)
print "The final sum of addfunc is: " + str(addsum)

When I run filename.py 2 2, does argv put 2 2 into strings? If so, how do I convert these into integers?

Thanks for your help.

Answer

Martijn Pieters picture Martijn Pieters · Jun 29, 2013

sys.argv is indeed a list of strings. Use the int() function to turn a string to a number, provided the string can be converted.

You need to assign the result, however:

num1 = int(argv[1])
num2 = int(argv[2])

or simply use:

num1, num2 = int(num1), int(num2)

You did call int() but ignored the return value.

Related questions

An integer is required? open()

I have a very simple python script that should scan a text file, which contains lines formatted as id='value' and put them into a dict. the python module is called chval.py and the input file is in.txt. …

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

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 …

Read More
from sys import argv - what is the function of "script"

I am reading "Learn Python the Hard Way" and was confused by the "script" part of the second line. from sys import argv script, filename = argv From what I understand, the second line says: script and filename comprise argv. I …

Read More