在 Python 模块中导入子模块

Question

I have already read Python: importing a sub‑package or sub‑module but this:

file                                content
============================================================================
main.py                             from mymodule.a import A; A()
mymodule/submodule/__init__.py      (empty)
mymodule/submodule/b.py             class B: pass
mymodule/__init__.py                (empty)
mymodule/a.py                       (see below)

mymodule/a.py :

import submodule
class A:
    def __init__(self):
        self.b = submodule.B()

fails with:

File "a.py", line 1, in
import submodule
ModuleNotFoundError: No module named 'submodule'

when lauching the script main.py .

Question: how should I import submodule in mymodule/a.py ?

Answer 1

TLDR:

mymodule/a.py :

from . import submodule
# or
import mymodule.submodule as submodule

Once you run your main.py , python adds to your sys.path the path to main.py folder. Python can now search subfolders to find modules trying to be imported. Once you import a.py , python DOES NOT add anything else to sys.path , therefore, to be able import subfolders, you need to do either relative importing ( from . import submodule ), which you can do because you aren't running a.py as your main file, OR do a full import, doing import mymodule.submodule , since python can search starting on main.py folder.