arr .__ len __()是在Python中获取数组长度的首选方法吗? [英] Is arr.__len__() the preferred way to get the length of an array in Python?

问题描述

在 Python 中，以下是获取数量的唯一方法元素?

In Python, is the following the only way to get the number of elements?

arr.__len__()

如果是这样，为什么使用奇怪的语法?

If so, why the strange syntax?

推荐答案

my_list = [1,2,3,4,5]
len(my_list)
# 5

对元组也是如此:

my_tuple = (1,2,3,4,5)
len(my_tuple)
# 5

还有字符串，它们实际上只是字符数组:

And strings, which are really just arrays of characters:

my_string = 'hello world'
len(my_string)
# 11

这是__len__()方法的所有内容的len().

It was intentionally done this way so that lists, tuples and other container types or iterables didn't all need to explicitly implement a public .length() method, instead you can just check the len() of anything that implements the 'magic' __len__() method.

当然，这似乎是多余的，但是长度检查的实现可能会有很大差异，即使使用相同的语言也是如此.经常看到一种集合类型使用.length()方法，而另一种类型使用.length属性，而另一种类型使用.count()并不少见.使用语言级别的关键字可以统一所有这些类型的入口点.因此，即使您可能不认为是元素列表的对象仍然可以进行长度检查.这包括字符串，队列，树等.

Sure, this may seem redundant, but length checking implementations can vary considerably, even within the same language. It's not uncommon to see one collection type use a .length() method while another type uses a .length property, while yet another uses .count(). Having a language-level keyword unifies the entry point for all these types. So even objects you may not consider to be lists of elements could still be length-checked. This includes strings, queues, trees, etc.

len()的功能本质也很适合于编程的功能样式.

The functional nature of len() also lends itself well to functional styles of programming.

lengths = map(len, list_of_containers)

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