Python-使用父包的__init__子模块

Question

I have a package structure as:

parent_package/
    __init__.py
    module/
        __init__.py

In the parent __init__.py I have:

from __future__ import division

print(3/2) # 1.5

However, when I tried to reuse the import in its child, division does not take effect. In module's __init__.py :

from parent_package.__init__ import division

print(3/2) # 1!

Answer 1

You are misunderstanding how the __future__ module works. __future__ is a special module that is built into the python interpreter and changes how the interpreter parses and/or executes your code. In order for a __future__ import to have the desired effect, it must be of the form

from __future__ import <feature>

(See PEP 236 for the exact specification.)

However, in addition to the __future__ module that's built into the interpreter, __future__ is also a real module in the standard library ! The import from __future__ import divison actually does two things: It enables the new division behavior, and it imports the feature specification from the real __future__ module. This is what you'll see if you take a look at the value of division after the import:

>>> from __future__ import division
>>> division
_Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192)

When you do from parent_package.__init__ import division , you're simply importing this variable. But you're not enabling the new division behavior.