[英]What's the purpose of the “__package__” attribute in Python?
All I want to know is what exactly does __package__
mean ? 我想知道的是__package__
究竟是什么意思 ? Didn't find any explanation in the official doc, even on SO. 在官方文件中没有找到任何解释,即使是在SO上。
If you could provide some examples I would be very happy. 如果你能提供一些例子,我会非常高兴。
See the PEP 366 and import system reference documentation : 请参阅PEP 366并导入系统参考文档 :
The major proposed change is the introduction of a new module level attribute,
__package__
. 主要的建议更改是引入新的模块级属性__package__
。 When it is present, relative imports will be based on this attribute rather than the module__name__
attribute. 如果存在,相对导入将基于此属性而不是模块__name__
属性。
and 和
- The module's
__package__
attribute should be set. 应该设置模块的__package__
属性。 Its value must be a string, but it can be the same value as its__name__
. 它的值必须是一个字符串,但它可以是与__name__
相同的值。 If the attribute is set toNone
or is missing, the import system will fill it in with a more appropriate value. 如果该属性设置为“None
或缺少,则导入系统将使用更合适的值填充该属性。 When the module is a package, its__package__
value should be set to its__name__
. 当模块是包时,其__package__
值应设置为__name__
。 When the module is not a package,__package__
should be set to the empty string for top-level modules, or for submodules, to the parent package's name. 当模块不是包时,__package__
设置为顶级模块的空字符串,或子模块的空字符串,设置为父包的名称。 See PEP 366 for further details. 有关详细信息,请参阅PEP 366 。
So, for a module located in foo/bar/baz.py
, __name__
is set to foo.bar.baz
, and __package__
is set to foo.bar
, while foo/bar/__init__.py
will have foo.bar
for both the __name__
and __package__
attributes. 因此,对于位于模块foo/bar/baz.py
, __name__
设为foo.bar.baz
,并__package__
设置为foo.bar
,而foo/bar/__init__.py
将有foo.bar
同时为__name__
和__package__
属性。
All I want to know is what exactly does
__package__
mean 我想知道的是__package__
究竟是什么意思
It is the mechanism that enables explicit relative imports. 它是实现显式相对导入的机制。
There are three possible categories of values for __package__
__package__
有三种可能的值类别
That is, if a module is in a package, __package__
is set to the package name to enable explicit relative imports. 也就是说,如果模块位于包中,则__package__
将设置为包名称以启用显式相对导入。 Specifically: 特别:
When the module is a package, its
__package__
value should be set to its__name__
. 当模块是包时,其__package__
值应设置为__name__
。 When the module is not a package,__package__
should be set [...] for submodules, to the parent package's name. 当模块不是包时,应将子模块的__package__
设置为父包的名称。
If a module is at root, or top-level, that is, the current module is imported with 如果模块位于root或top级别,即导入当前模块
import current_module
or when a top-level module is run as the entry point as with: 或者当顶级模块作为入口点运行时,如下所示:
$ python -m current_module
then __package__
is an empty string. 那么__package__
是一个空字符串。 Or as the documentation says : 或者正如文档所说 :
When the module is not a package,
__package__
should be set to the empty string for top-level modules... 当模块不是包时,__package__
应该设置为顶级模块的空字符串...
If a module/script is run by filename, __package__
is None : 如果模块/脚本由filename运行, __package__
为None :
When the main module is specified by its filename, then the
__package__
attribute will be set to None. 当主模块由其文件名指定时,__package__
属性将设置为None。
First, let's create a file structure with noisy debugging - using Python 3.6: 首先,让我们使用Python 3.6创建一个带有嘈杂调试的文件结构:
text = "print(f'{__name__}, __file__: {__file__}, __package__: {repr(__package__)}')"
from pathlib import Path
Path('foo.py').write_text(text)
Path('package').mkdir()
Path('package/__init__.py').write_text(text)
Path('package/__main__.py').write_text(text)
Path('package/bar.py').write_text(text)
# and include a submodule with a relative import:
Path('package/baz.py').write_text(text + '\nfrom . import bar')
Now we see that foo.py executed as a module has an empty string for __package__
, while the script executed by file name as the entry point has None
: 现在我们看到作为模块执行的foo.py具有__package__
的空字符串,而由文件名作为入口点执行的脚本具有None
:
$ python -m foo
__main__, __file__: ~\foo.py, __package__: ''
$ python foo.py
__main__, __file__: foo.py, __package__: None
When we execute a package as a module for the entry point, its __init__.py
module runs, then its __main__.py
runs: 当我们执行一个包作为入口点的模块时,它的__init__.py
模块运行,然后它的__main__.py
运行:
$ python -m package
package, __file__: ~\package\__init__.py, __package__: 'package'
__main__, __file__: ~\package\__main__.py, __package__: 'package'
Similarly, when we execute a submodule as a module for the entry point, the __init__.py
module runs, then it runs: 类似地,当我们执行子模块作为入口点的模块时,运行__init__.py
模块,然后运行:
$ python -m package.bar
package, __file__: ~\package\__init__.py, __package__: 'package'
__main__, __file__: ~\package\bar.py, __package__: 'package'
Finally, we see that the explicit relative import, the entire reason for having __package__
, (which happens last here) is enabled: 最后,我们看到显式相对导入,具有__package__
的完整原因(在此处发生)将启用:
$ python -m package.baz
package, __file__: ~\package\__init__.py, __package__: 'package'
__main__, __file__: ~\package\baz.py, __package__: 'package'
package.bar, __file__: ~\package\bar.py, __package__: 'package'
Note, in the output, I have substituted ~
for the parent directories. 注意,在输出中,我已经用~
替换了父目录。
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