导入后属性未添加到模块 [英] Attribute not added to module after importing

问题描述

我做了以下实验:

vagrant@ubuntu-xenial:~/test$ tree
.
├── pack1
│   ├── __init__.py
│   ├── mod1.py
│   └── pack2
│       ├── __init__.py
│       ├── mod2.py
│       └── mod3.py
└── test.py

2 directories, 6 files
vagrant@ubuntu-xenial:~/test$ tail -n +1 *.py */*.py */*/*.py
==> test.py <==
#!/usr/bin/python
import pack1.pack2.mod2
print(__file__)
try:
    print(pack1.__dict__['pack2'])
except Exception as error:
    print("MISSING PACK2")

==> pack1/__init__.py <==

==> pack1/mod1.py <==

==> pack1/pack2/__init__.py <==
import pack1.pack2.mod2

==> pack1/pack2/mod2.py <==
import pack1.pack2.mod3
print(__file__)
try:
    print(pack1.__dict__['pack2'])
except Exception as error:
    print("MISSING PACK2")

==> pack1/pack2/mod3.py <==
vagrant@ubuntu-xenial:~/test$ ./test.py
/home/vagrant/test/pack1/pack2/mod2.py
MISSING PACK2
./test.py
<module 'pack1.pack2' from '/home/vagrant/test/pack1/pack2/__init__.py'>
vagrant@ubuntu-xenial:~/test$

在导入pack1.pack2.mod3之后，pack2不是pack1/pack2/mod2.py中pack1的属性.

pack2 is not an attribute of pack1 within pack1/pack2/mod2.py after importing pack1.pack2.mod3.

但是，当pack1/pack2/__ init__.py 不导入pack pack1.pack2.mod2时，此方法有效.

It works, however, when the pack1/pack2/__init__.py does not import pack pack1.pack2.mod2.

这是为什么?

推荐答案

当模块的导入完成时，会将模块作为其包的属性添加. (请注意，这可能会干扰循环的相对导入.)在这里，pack2立即导入mod2，因此(不管像mod3这样的进一步完成的导入)，在pack1词典中它都不会出现在mod2的执行.

A module is added as an attribute of its package when its import finishes. (Note that this can interfere with circular relative imports.) Here, pack2 immediately imports mod2, so (regardless of further completed imports like that of mod3) it doesn’t appear in the pack1 dictionary during mod2’s execution.

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