how to add a package to sys path for testing

This question is occasioned by instructions in the python guide for adding a project to sys path to use in tests, which do not seem to work unless I am misunderstanding the instructions

I have a directory structure for a python project like this

sample/a.py
sample/b.py
sample/c.py
sample/__init__.py
test/context.py
test/test_something.py
test/__init__.py
docs

According to the python guide, I should create a test/context.py file and add this

import os
import sys
sys.path.insert(0, os.path.abspath('..'))

import sample

Then, in my test/test_something.py file, it says I can do this

from .context import sample

The guide says “This will always work as expected”.

but, when I cd into test and run

python -m unittest test_something

I get an error

ValueError: Attempted relative import in non-package

and the error message specifically refers to this: from .context import sample

Question: How can I add my sample package to the sys path correctly?

When answering, can you also clarify if the solution will handle absolute imports within the sample package. For example, my sample.a imports sample.b etc. When I had my tests structured a different way, I did an absolute import of sample.a, but since it has a relative import of from .b import Boo, it produced a similar error

Update

`File "/usr/local/lib/python2.7/runpy.py", line 162 in _run_module_as_main "__main__", fname, loader, pkg_name)
File  "/usr/local/lib/python2.7/runpy.py", line 72, in _run_code exec code in run_globals
File  "/usr/local/lib/python2.7/unittest/__main__.py", line 12, in module main(module=None)
File  "/usr/local/lib/python2.7/unittest/main.py", line 94, in __init__ self.parseArgs(argv)
File  "/usr/local/lib/python2.7/unittest/main.py", line 149 in parseArgs self.createTests()
File  "/usr/local/lib/python2.7/unittest/main.py", line 158, in createTests self.module)
File  "/usr/local/lib/python2.7/unittest/loader.py", line 130, in loadTestsFromNames suites = [self.loadTestsFromName(name,module) for name in names]
File  "/usr/local/lib/python2.7/unittest/loader.py", line 91, in loadTestsFromName module = __import__('-'.join(parts_copy))
File "test_something.py", line 8, in module from .context import sample

Update

if I run the following command from root directory

   python -m unittest test

It says , “Ran 0 tests in 0.000s”

If, as was suggested in the comments by @cuongnv, I run this from root directory

python -m unittest test/test_something.py

or this (without the file extension)

python -m unittest test/test_something 

It says “Import by filename is not supported”

Answer

Question: How can I add my sample package to the sys path correctly?

You’re doing it the right way, but you missed declaring your folder to be a package. Try solution of Christian, it should work.

Your path is stored in sys.path. By doing this:

sys.path.insert(0, os.path.abspath('..'))

You’re telling your python to add upper folder (of current file) into your path. As sys.path is a list, you can using other methods of list like insert, append…

In your case, you’re inserting your upper dir at top of the path list.

See:

In [1]: import sys

In [2]: sys.path
Out[2]: 
['',
 '/usr/local/bin',
 '/usr/lib/python3.4',
 '/usr/lib/python3.4/plat-x86_64-linux-gnu',
 '/usr/lib/python3.4/lib-dynload',
 '/usr/local/lib/python3.4/dist-packages',
 '/usr/lib/python3/dist-packages',
 '/usr/local/lib/python3.4/dist-packages/IPython/extensions',
 '/home/cuong/.ipython']

In [3]: sys.path.insert(0, '/tmp/foo')

In [4]: sys.path
Out[4]: 
['/tmp/foo', **<-- on top**
 '',
 '/usr/local/bin',
 '/usr/lib/python3.4',
 '/usr/lib/python3.4/plat-x86_64-linux-gnu',
 '/usr/lib/python3.4/lib-dynload',
 '/usr/local/lib/python3.4/dist-packages',
 '/usr/lib/python3/dist-packages',
 '/usr/local/lib/python3.4/dist-packages/IPython/extensions',
 '/home/cuong/.ipython']

So, from here, when you have

import sample

your python will try to look in path to see if there is any sample package.

Unfortunately, it can’t find sample as you didn’t make it as a package because your forgot __init__.py in sample folder.

Hope my explanation would help you to understand and you can handle other situations different to this.