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

2

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])

answered Jan 1, 2014 at 20:34

ApproachingDarknessFish

14.4k8 gold badges42 silver badges81 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

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

1

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])

answered Jan 1, 2014 at 20:45

Dyrborg

8777 silver badges16 bronze badges

2 Comments

Guilherme Over a year ago

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[]?

Dyrborg Over a year ago

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.

Collectives™ on Stack Overflow

How to read user input in Python

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related