Python的__loader__是什么? [英] Python's __loader__, what is it?

问题描述

我已经看到 __ loader __ 这个术语在一些Python文件中不停地浮动，除了一些简短的目的描述之外，我找不到任何文档，但是它们仍然不能提供足够的信息信息使我对它有很好的了解.我所知道的是，它与导入模块有关，除了我完全不知所措.它有什么作用?什么时候使用?怎么可以使用它?

I've seen the term __loader__ floating around some Python files and I can't find any documentation on it aside from a few brief descriptions about it's purpose, but they still don't provide enough information for me to get a good understanding of it. All I know is that it has something to do with importing modules, other than that I'm completely at a loss. What does it do? When is it used? How can I use it if at all?

推荐答案

什么是 __ loader __ ?

__ loader __ 是由其加载器在导入的模块上设置的属性.访问它应该返回加载程序对象本身.

__loader__ is an attribute that is set on an imported module by its loader. Accessing it should return the loader object itself.

在3.3之前的Python版本中，内置导入机制未设置 __ loader __ .相反，该属性仅在使用自定义加载程序导入的模块上可用.

In Python versions before 3.3, __loader__ was not set by the built-in import machinery. Instead, this attribute was only available on modules that were imported using a custom loader.

但是，由于 PEP 0302 ，此功能在Python 3.3中发生了变化.现在， __ loader __ 在每个导入的模块上都可用:

However, this functionality changed in Python 3.3 because of PEP 0302. Now, __loader__ is available on every module that is imported:

>>> # Python 3.3 interpreter
>>> import os
>>> os.__loader__
<_frozen_importlib.SourceFileLoader object at 0x01F86370>
>>>

---

什么是装载机?

加载程序是查找程序返回的对象.它使用其 load_module()方法将模块加载到内存中. importlib.abc.Loader 是以下示例加载程序的抽象基类.

A loader is an object that is returned by a finder. It uses its load_module() method to load a module into memory. importlib.abc.Loader is an example of an abstract base class for a loader.

什么是取景器?

查找器是使用其 find_module()的对象>尝试找到模块加载程序的方法. importlib.abc.Finder 是以下示例查找器的抽象基类.但是请注意，不推荐使用 importlib.abc.MetaPathFinder 和> importlib.abc.PathEntryFinder .

A finder is an object that uses its find_module() method to try and find the loader for a module. importlib.abc.Finder is an example of an abstract base class for a finder. Note however that it is deprecated in favor of importlib.abc.MetaPathFinder and importlib.abc.PathEntryFinder.

我怎么使用它?

__ loader __ 的主要用途是自省.但是，还有其他两种常见用法:

The main use of __loader__ is for introspection. However, there are two other common uses:

1. __loader__ 可用于收集特定模块加载器的数据.

1. __loader__ may be used to gather data on a specific module's loader.

在3.3之前的Python版本中，可以将 __ loader __ 与 hasattr 一起使用，以检查是否已使用内置导入机制导入了模块:

In Python versions before 3.3, __loader__ could be used with hasattr to check whether or not a module was imported with the built-in import machinery:

>>> # Python 3.2 interpreter
>>> import os
>>> hasattr(os, '__loader__')
False
>>>

如果 hasattr(os，'__loader __')返回了 True ，则表示 os 模块是使用自定义加载程序导入的.既然没有，则意味着该模块是使用内置的导入机制导入的.

If hasattr(os, '__loader__') had returned True, it would mean that the os module was imported using a custom loader. Since it did not, it means that the module was imported using the built-in import machinery.

注意:由于PEP 0302所做的更改，以上测试在Python 3.3+中将不起作用.

Note: The above test will not work in Python 3.3+ because of the changes made by PEP 0302.

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