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.