python中导入模块的歧义

Question

I have a Python library that looks like this (contains packages):

|-- python_lib/
    |-- plotting.py
    |-- verification.py
    |-- io.py
    |
    |-- ensemble/
        | -- plotting.py
        | -- verification.py

However, I am having problems with ambiguous module imports. In ensemble.plotting.py I want to import the verification.py module from the top level ( python_lib ):

# ensemble/plotting.py
import verification.obs as verobs

However, I get an import error as this tries to import the verification.py module from the ensemble directory, rather than the top level of the library.

I thought that the "abslute imports" feature would solve this:

from ..verification import obs

but I get this error:

ValueError: Attempted relative import beyond toplevel package

How do I target python_lib/verification.py as an import from python_lib/ensemble/*.py without trying to import the local package version?

I am using Python version 2.7.

Answer 1

1. All your directories should contain files __init__.py , or they won't be recognized as packages.

2. Your directory python_lib must be a known path. You said in a comment that your PYTHONPATH contains a path to python_lib , so that seems good.

3. If you start with eg python_lib/ensemble/verification.py as your main entry point, then the directory python_lib/ensemble shadows your directory python_lib , and you have to manually tell Python that your script belongs to that package.

Like this:

 if __name__ == "__main__" and __package__ is None:
     __package__ = "pythonlib.ensemble"
     import pythonlib

After that is done, this should work:

from ..verification import obs

Answer 2

It's a hacky solution that would work but is generally discouraged.

You can modify python path in place when you have to omit conflicts. Like that:

import sys  # needed to make it work

tmp = sys.path[0]
sys.path = sys.path[1:]  # ugly and hacky thingy

# import stuff you need (would work with __init__.py in a base dir)
from python_lib import verification
from ..verification.obs import obs

# fix path back
sys.path.insert(0, tmp)

I just tested this pattern and it seems to work (Python 3.6.0)

Answer 3

There are some rules that has to be followed while creating packages and modules.

1. Make sure there is __init__.py file as a part of your package. Every python package is expected to have this file
2. While the module is looked it happens in 3 ways.

A very good documentation is available Module-search-path

Usually while building projects it a practice to create a lib package and add sub directories based on different categories and add the main directory to the PYTHONPATH variable. This make the module available for other programs.