How to properly set the path to input/output file?

Question

I am working on part of a Python project and the structure is like this: project/some_folder/another_folder/my_work.

In this folder, the file containing the code is run.py. In the same folder, I also have an input_file from which I read some data, process it, and write the result to output_file. So in run.py I have something like:

with open("input_file") as f:
    do_something()

and

with open("output_file") as f:
    store_the_result()

This works fine when I execute the code in project/some_folder/another_folder/my_work. However, when I go to project and run the code using python -m some_folder.another_folder.my_work.run, I will have trouble accessing the input file. I tried to solve this problem by using the aboslute path to the files, but this will only work on my machine. If someone copies my code to his/her machine, he/she still needs to modify the hardcoded absolute path.

How to set the path to the files such that I can start the program either in the folder containing the input and output file, or run it as a module, and others will not need to modify the path to the file when running code on their machines?

s9527 · Accepted Answer · 2017-07-11 09:48:08Z

6

You can get the path to the running module and then create a full path relatively from there:

import os

module_path = os.path.dirname(os.path.realpath(__file__))

input_path = os.path.join(module_path, 'input_file')
output_path = os.path.join(module_path, 'output_file')

with open(input_path) as f:
    do_something()

with open(output_path) as f:
    store_the_result()

edited Jul 11, 2017 at 9:48

s9527

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answered Jul 11, 2017 at 8:58

Paco H.

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6 Comments

s9527 Over a year ago

module_path = os.path.dirname(os.path.realpath(__file__)) doesn't work for me. I need to use module_path = os.path.dirname(os.path.realpath("__file__")) instead.

Paco H. Over a year ago

That's strange, if I use "__file__" (using quotes) then i get the current working directory, not the module directory. What's more, using "__file__" gives me the same result as using "__some_random_string__". When you say that it doesn't work you mean that it throws an error?

s9527 Over a year ago

In my case, "__file__" will also give the CWD, but __file__ simply throws NameError: name '__file__' is not defined.

Paco H. Over a year ago

Are you running it from python interactive shell? If so that's the problem.

s9527 Over a year ago

Yes I am. I will try to run it in the normal mode.

|

rabbit · Accepted Answer · 2017-07-11 09:11:13Z

1

If you do not explicitly specify the "input_file" path, Python assumes that it resides in the current directory in which you are executing your Python script. The answer given by Paco H should solve the problem.

answered Jul 11, 2017 at 9:11

rabbit

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