无法在同一 package 中导入 Python 模块

Question

I have a Python 3.9.2 project with the following directory structure:

lib/
├─ mod1.py
├─ mod2.py
├─ __init__.py
main.py

In /main.py , I have from lib import mod1 . In /lib/mod1.py , I have import mod2 . When I run /main.py , I receive the following error:

Traceback (most recent call last):
  File "/main.py", line 1, in <module>
    from lib import mod1
  File "/lib/init.py", line 1, in <module>
    import mod2
ModuleNotFoundError: No module named 'mod2'

Why is this happening? When I change the code in /lib/mod1.py to say from lib import mod2 , the code works fine, but I don't understand why that fixes it. Shouldn't I be able to import /lib/mod2.py the way I originally tried, since both mod1.py and mod2.py are in the same directory?

Answer 1

In /lib/mod1.py , you probably want to do:

# relative import - entire module
from . import mod2

# relative import - specific piece
from .mod2 import foo 

or

# absolute import - entire module
from lib import mod2

# absolute import - specific piece
from lib.mod2 import foo

The correct way to import things is really tricky in Python because it depends on where you run the script from.

• If you run the code from the root directory, import mod2 causes problems, but
• If you were to run /lib/mod1.py (say it were run-able) from inside lib , then import mod2 would be correct and the alternatives above would cause errors.