How can I set an "input" in a Python function automatically?

Question

So in case the above question doesn't make any sense, I have a function in Python (not written by me but I have to run it many times) that requires the use of the "input" function. I.e.

def foo():
    x = input()
    ~~Do stuff~~
    return ~~some relevant variable~~

But I don't want to have to type in the input every single time. What is the best way to "automatically" enter an input such that I don't have to continually input the values?

Important Edit: Its very important to note that I cannot change the function. The thing must be entered as an STDIN input

Pass the value to the function as a parameter? It kind of depends on what you're doing with it. — Patrick Haugh
– Patrick Haugh, Commented Oct 16, 2017 at 17:36
Just have the function return the value you would have manually entered and skip the call to input — pvg
– pvg, Commented Oct 16, 2017 at 17:37
I just edited it to specify that I can't change the internals of the function. It works how it works — wjmccann
– wjmccann, Commented Oct 16, 2017 at 17:38
Put the text in a file and invoke the script redirecting the input from that file. — kindall
– kindall, Commented Oct 16, 2017 at 17:38
Was about to say the same as @kindall . that's the easiest way to go about it keeping the function same. — Kaushik NP
– Kaushik NP, Commented Oct 16, 2017 at 17:40

martin · Accepted Answer · 2017-10-16 17:39:56Z

10

You can change the standard input by a string stream or a file by doing something similar to this:

import sys
from io import StringIO

sys.stdin = StringIO('test')

Then each call to input() will get the value on the string stream.

EDIT: You can then read a file and update the value of sys.stdin each time with a value per line.

answered Oct 16, 2017 at 17:39

martin

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juanpa.arrivillaga · Accepted Answer · 2017-10-16 17:57:28Z

4

I highly, highly suggest you implement a context manager, and strictly use this context manager whenver you want to do this. So, something like:

import sys

class as_stdin:
    def __init__(self, buffer):
        self.buffer = buffer
        self.original_stdin = sys.stdin
    def __enter__(self):
        sys.stdin = self.buffer
    def __exit__(self, *exc):
        sys.stdin = self.original_stdin

Then you can redirect your stdin in a much more tightly controlled way:

>>> import io
>>> from redirect import as_stdin
>>> def echo():
...     print(input())
...
>>> with as_stdin(io.StringIO('hello, world')):
...     echo()
...
hello, world
>>> x = input()
hello, x
>>>
>>> print(x)
hello, x

answered Oct 16, 2017 at 17:57

juanpa.arrivillaga

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