Importing a class in another folder

Question

I have a problem with python directories.

I have structure like:

• python
  • modules
    • algorithms
      • cyphers
        • morse.py
  • tests
    • algorithms
      • cyphers
        • test_morse.py

When I try to import module in test I get a module not found error. I am trying to import like:

parent_dir_name = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
sys.path.append(parent_dir_name + "/../../../")

from modules.algorithms.cyphers.morse import *

I have also init files in all directories. I am trying to run tests like:

> python -m unittest discover ./tests

Answer 1

It is customary to use relative imports

from ....modules.algorithms.ciphers.morse import *

This ensures that you import the right Morse file, otherwise you risk importing some module named Morse that you've installed.

Here's two examples to illustrate relative imports, say you have a file named simulation.py that has the line

from .animals import Herbivore

In it. This will import the Herbivore class from a file in the same directory as the simulation.py file

Now imagine that you are a folder named tests, in this folder you have a file named test_animals.py, which has the line

from ..animals import Herbivore

This will import the Herbivore class from a file named animals.py located in the folder above the tests folder.

Finally, note that (at least for Python 3.6) can't run a file that uses relative imports, only import it.

Answer 2

如果使用__init__.py将目录标记为模块，则应该能够通过导入模块

from modules.algorithms.cyphers import morse