类/函数定义中的导入语句 - 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/函数定义中导入所需内容的优缺点是什么?它比模块文件开头的 import 更好吗?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

将 every 导入放在文件顶部是最常见的样式.PEP 8 推荐它，这是开始做它的一个很好的理由.但这不是心血来潮，它具有优势(尽管还不足以使其他一切都成为犯罪).它允许一目了然地找到所有导入，而不是查看整个文件.它还确保在执行任何其他代码(可能取决于某些导入)之前导入所有内容.NameError 通常很容易解决，但它们可能很烦人.

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.

将模块保持在较小的范围内不会避免(显着的)命名空间污染，因为您添加的只是实际模块(不，import * 不算数，可能也不应该使用).在函数内部，您会在每次调用时再次导入(并不是真的有害，因为所有内容都导入一次，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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