Python导入 [英] Python importing

问题描述

我有一个文件myfile.py，它从file.py导入Class1，并且file.py包含对file2.py，file3.py，file4.py的不同类的导入.

I have a file, myfile.py, which imports Class1 from file.py and file.py contains imports to different classes in file2.py, file3.py, file4.py.

在我的myfile.py中，我可以访问这些类吗?还是需要再次导入file2.py，file3.py等?

In my myfile.py, can I access these classes or do I need to again import file2.py, file3.py, etc.?

Python是否会自动添加我导入的文件中包含的所有导入，并且我可以自动使用它们吗?

Does Python automatically add all the imports included in the file I imported, and can I use them automatically?

推荐答案

最佳实践是导入定义所需标识符的每个模块，并使用该模块名称通过限定的标识符；我建议仅在要导入的是软件包中的模块时才使用from.这个问题经常在SO上讨论.

Best practice is to import every module that defines identifiers you need, and use those identifiers as qualified by the module's name; I recommend using from only when what you're importing is a module from within a package. The question has often been discussed on SO.

从需要一个或多个moda定义的标识符的许多模块(例如modb，modc，modd，...)中导入一个模块，例如moda，不会降低您的速度down:moda的字节码仅加载一次(并且可能从其源代码构建，如果需要)，第一次将moda导入任何地方，然后模块的所有其他导入都使用涉及缓存的快速路径( dict将模块名称映射到可以在需要的情况下通过sys.modules访问的模块对象...，如果您首先是import sys，当然！-).

Importing a module, say moda, from many modules (say modb, modc, modd, ...) that need one or more of the identifiers moda defines, does not slow you down: moda's bytecode is loaded (and possibly build from its sources, if needed) only once, the first time moda is imported anywhere, then all other imports of the module use a fast path involving a cache (a dict mapping module names to module objects that is accessible as sys.modules in case of need... if you first import sys, of course!-).

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