在 Python 中导入深度嵌套的模块

问题描述

考虑 Python 3.6 中的以下情况:

Consider the following case in Python 3.6:

basepackage
    |---__init__.py
    |---package
            |---__init__.py
            |---subpackage
                    |---__init__.py
                    |---module.py

重要细节:在 basepackage.package.__init__.py 里面有:

from basepackage.package.subpackage.module import AClass as AliasedClass

现在，让我们说在 basepackage.package.subpackage.module.py 中我们要使用:

Now, let's say inside basepackage.package.subpackage.module.py we want to use:

将 basepackage.package.subpackage.module 导入为 aliased_module [1]

结果是:

AttributeError: module 'basepackage' has no attribute 'package'

在罪魁祸首语句之后列出堆栈跟踪(按以下顺序):

with a stack trace listing following culprit statements (in the below order):

from basepackage.package.subpackage.module import AClass as AliasedClass
import basepackage.package.subpackage.module as aliased_module

但如果你想使用 [1] 而不是:

But if instead of [1] one'd like to use:

from basepackage.package.subpackage import module as aliased_module [2]

然后一切正常.

[1] 与 [2] 有何不同，前者会导致错误，而后者不会?

How is [1] so much different than [2] that the former results in an error and the latter not?

推荐答案

要使第一个选项(import basepackage.package.subpackage.module as aliased_module)起作用，必须满足以下条件:

For the first option (import basepackage.package.subpackage.module as aliased_module) to work, these conditions have to be met:

• basepackage/__init__.py 必须包含类似于 from 的行.import package(名称package必须在这个basepackage/__init__.py文件中定义)
• basepackage/package/__init__.py 必须包含类似于 from 的行.导入子包
• basepackage/package/subpackage/__init__.py 必须包含类似于 from 的行.导入模块

• basepackage/__init__.py has to contain a line similar to from . import package (the name package has to be defined inside this basepackage/__init__.py file)
• basepackage/package/__init__.py has to contain a line similar to from . import subpackage
• basepackage/package/subpackage/__init__.py has to contain a line similar to from . import module

注意:__init__.py 文件中的 import 语句也可以是绝对路径而不是相对路径.

Note: the import statements inside the __init__.py files can also be absolute instead of relative paths.

对于第二个选项(from basepackage.package.subpackage import module as aliased_module)，如果每个级别都有空的 __init__.py 文件就足够了，如只要这些 __init__.py 文件存在.

For the second option (from basepackage.package.subpackage import module as aliased_module), it is enough if there are empty __init__.py files at each level, as long as these __init__.py files exist.

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