import语句里面的类/函数定义 - 这是一个好主意吗？ [英] Import statement inside class/function definition - is it a good idea?

问题描述

我创建了一个名为 util 的模块，它提供了我经常在Python中使用的类和函数。
其中一些需要导入功能。在类/函数定义中导入需要的东西的优点和缺点是什么？在模块文件的开头是否优于 import ？这是个好主意吗？

I created a module named util that provides classes and functions I often use in Python. Some of them need imported features. What are the pros and the cons of importing needed things inside class/function definition? Is it better than import at the beginning of a module file? Is it a good idea?

推荐答案

这是最常见的风格，的文件。 PEP 8推荐它，这是一个很好的理由做它开始。但这不是一个奇迹，它有优点（虽然不是至关重要，使一切都犯罪）。它允许一目了然地查找所有导入，而不是查看整个文件。它还确保在任何其他代码（可能依赖于某些导入）被执行之前导入一切。 NameError 通常很容易解决，但他们可以讨厌。

It's the most common style to put every import at the top of the file. PEP 8 recommends it, which is a good reason to do it to start with. But that's not a whim, it has advantages (although not critical enough to make everything else a crime). It allows finding all imports at a glance, as opposed to looking through the whole file. It also ensures everything is imported before any other code (which may depend on some imports) is executed. NameErrors are usually easy to resolve, but they can be annoying.

没有通过将模块保持在较小的范围内来避免，因为您添加的是实际模块（否， import * 不计数，可能不应该使用）。在内部函数中，您将在每次调用时重新导入（不是真正有害的，因为一切都导入一次，但不需要）。

There's no (significant) namespace pollution to be avoided by keeping the module in a smaller scope, since all you add is the actual module (no, import * doesn't count and probably shouldn't be used anyway). Inside functions, you'd import again on every call (not really harmful since everything is imported once, but uncalled for).

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