Python import precedence: packages or modules?

问题:

I wasn't clear how to correctly name this question.

Case 1

Assume that I have the following directory structure.

foo
|
+- bar/__init__.py
|
+- bar.py

If I have

from foo import bar

How do I know which bar (bar.py or bar/__init__.py) is being imported? Is there any easy way to automatically detect this from occurring?

Case 2

foo
|
+- foo.py
|
+- other.py

If other.py has the line

import foo

How do I know which foo (foo or foo.foo) is being imported? Again, is tehre any easy way to automatically detect this from occurring?

回答1:

TLDR; a package takes precedence over a module of the same name if they are in the same directory.

From the docs:

"When a module named spam is imported, the interpreter searches for a file named spam.py in the current directory, and then in the list of directories specified by the environment variable PYTHONPATH. This has the same syntax as the shell variable PATH, that is, a list of directory names."

This is a bit misleading because the interpreter will also look for a package called spam (a directory called spam containing an __init__.py file). Since the directory entries are sorted before searching, packages take precedence over modules with the same name if they are in the same directory because spam comes before spam.py.

Note that "current directory" is relative to the main script path (the one where __name__ == '__main__' is True). So if you are at /home/billg calling /foo/bar.py, "current directory" refers to /foo.

回答2:

from a python shell:

from foo import bar

print bar.__file__

should tell you which file has been imported

Rob

回答3:

Packages (directories with __init__.py) take precedence over modules. The documentation of this fact is difficult to find but you can see this in the source: python 2.7, python 3.6 (thanks @qff for the find).

You will also need a __init__.py within the foo directory for your example to work.

If other.py is inside of foo/ then it will load foo.py (not the directory foo/) because it will look in the current directory first (unless you've played with PYTHONPATH or sys.path).

回答4:

in the first case you're trying to import the function bar from file 'foo.py'

In the second you're trying to import the file 'foo.py'