How do I import files in Python?

Question

I'm trying to use pytest to check a function—here is my code:

# src/return_self.py
def return_self(n):
    return n


# tests/return_self_test.py
import pytest

def test_1():
    value = return_self(1)
    assert value == 1

How do I require in my src file so that I can test it with pytest? I have tried a few things:

1. import return_self
2. from src.return_self import *
3. import sys
   sys.path.append('../src')
4. import imp
   return_self = imp.load_source('return_self', '/source/return_self.py')

I have also tried them with and without __init__.py files in the root and src directories. But each time, I get some variation on the error E ModuleNotFoundError: No module named 'return_self'. How can I require in my file?

are `src/` and `tests/` in the same directory? – pythad Jul 08 '17 at 22:49 — pythad, Jul 08 '17 at 22:49

score 3 · Accepted Answer · answered Jul 08 '17 at 22:51

3

You can try this approach:

# tests/return_self_test.py

import os
import sys
import pytest

sys.path.insert(1, os.path.join(sys.path[0], '..'))

from src.return_self import return_self

def test_1():
    value = return_self(1)
    assert value == 1

answered Jul 08 '17 at 22:51

pythad

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Thanks, it works! I'm confused though—why does python require 5 lines to import a file? – achalk Jul 08 '17 at 23:01
1

@adc17, you can import things from directories on the system path, or the current directory, or subdirectories within a package. That why you need to add outer path to your system path in order to make python see your other folders – pythad Jul 08 '17 at 23:05
Thank you, so is my way of organising tests unusual? If I'm not following the right conventions please let me know. – achalk Jul 08 '17 at 23:07
1

@adc17, no, it's a good practice to place all tests in the `tests/` folder and until your module becomes a package, this importing is a little gotcha you need to know – pythad Jul 08 '17 at 23:13
Thanks @pythad, one last question. Do you know how this code imports the functions it needs without additional lines? https://github.com/AndyLPK247/automation-panda/tree/master/python-testing-101/example-py-pytest – achalk Jul 08 '17 at 23:29
@adc17, yes, they use `python -m ...` to run module inside the package. Take a look at https://stackoverflow.com/questions/72852/how-to-do-relative-imports-in-python for a discussion on this topic. – pythad Jul 08 '17 at 23:33
Thanks, `python -m pytest` is a great solution. – achalk Jul 09 '17 at 15:55

I'l Follio · Answer 2 · 2017-07-08T23:17:49.857

First, you must check that src/ and tests/ are in the same directory, I checked the function importing return_self in return_self_test.py and this is how:

Testpy search for files with test_[prefix] so I recommend changing return_self_test.py to test_return_self.py

# src/return_self.py
def return_self(n):
    return n


# tests/test_return_self.py
import return_self

def test_1():
    value = return_self.return_self(1)
    assert value == 1

Finally, test in cmd (in the correct path) or Pycharm terminal with the following command: py.test -v and voila! It's done (:

slackmart · Answer 3 · 2017-07-08T23:39:35.543

I will suggest you the setuptools approach (which makes your package distributable :D)

Project files' structure:

.
├── sample
│   ├── __init__.py
│   └── return_self.py
├── setup.cfg
├── setup.py
└── tests
    └── test_return_self.py

where the sample/ directory matches the package's name and also must contain the source.

Minimal setup.py file content:

from setuptools import setup

setup(
    setup_requires=['pytest-runner'],
    tests_require=['pytest'],
    name='sample'
)

Here we are configuring our test environment (you can extend the tests_require variable to include more testing requirements).

setup.cfg file content:

[aliases]
test=pytest

And here we specify we want to run the command pytest every time the developer does: python setup.py test

tests/test_return_self.py

from pytest import *

from sample.return_self import return_self

def test_return_self():
     assert return_self(4) == 4

sample/return_self.py

def return_self(n):
    return n

So, the next thing to do is to run:

python setup.py develop

to make your package available (while running the tests). If you're having problems with permission denied issues: append the --user option to the previous command to instruct python you wanna use the package without root permissions --in short the package will be installed into userland directories.

And finally run the tests using:

python setup.py test

Notes:

By using this approach, you'll be able to alter your project code on the fly (python setup.py develop needs to be run just once)
No ugly statements to inject the source directory into the current python path.

References:

Integrating with setuptools / python setup.py test / pytest-runner

Building and Distributing Packages with Setuptools

How do I import files in Python?

3 Answers3