How to read user input in Python

Question

I'm beginner in Python and I'm trying to read two numbers in a simple programming contest problem.

# Codeforces New Year 2013 Contest; # http://codeforces.com/contest/379/problem/A import sys; def main (): a = input (); b = input (); resto = 0; result = 0; while (a > 0): a-=1 result += 1; resto += 1; if (resto >= b): resto -= b; a += 1; print result; main ();

if I try to run the program with 4 2 (separated by a blank space), I get the following error:

ValueError: invalid literal for int() with base 10: '4 2'

But if I type 4 [enter] and then 2 [enter], the program runs without any problems.

How do I read from stdin in python just like C++ does?

Edit: Sorry for the mess! I usually run a code with input this way:

C++: ./main < test

Python: python main.py < test

I think you're confused with what constitutes standard input. Standard input is what's provided on the command line when you invoke the program. You're just reading what the user types in the prompt. — Dan Loewenherz
– Dan Loewenherz, Commented Jan 1, 2014 at 20:35

ApproachingDarknessFish · Accepted Answer · 2014-01-01 20:34:29Z

Based on your syntax, I assume you're using python 2.

Use raw_input to read a string from the console and then manually split it before parsing your ints:

s = raw_input() tokens = s.split() a = int(tokens[0]) b = int(tokens[1])

Dyrborg · Accepted Answer · 2014-01-01 20:45:12Z

You can use sys.argv which is similar to many other programming languages:

import sys for a in sys.argv: print a

If you invoke this program from the command line like this:

python test.py 10 20 30 40 50

Then it will print:

test.py 10 20 30 40 50

So you can just access your arguments using indexes:

print sys.argv[2] #prints 20

Remember though that sys.argv contains strings - so if you want to handle the input like integers remember to cast them first like this:

int(sys.argv[2])

Thanks, that's what I'm looking for. If I try to run the program using python test.py < input_file, all the content of the file goes to sys.argv[]?
No it will not. If I were you I would just run "python test.py input_file" and then open the file within the program itself.

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How to read user input in Python

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