Is arr.__len__() the preferred way to get the length of an array in Python?

Question

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

arr.__len__()

If so, why the strange syntax?

Answer 1

The preferred way to get the length of any python object is to pass it as an argument to the len function. Internally, python will then try to call the special __len__ method of the object that was passed.

Answer 2

The way you take a length of anything for which that makes sense (a list, dictionary, tuple, string, ...) is to call len on it.

l = [1,2,3,4]
s = 'abcde'
len(l) #returns 4
len(s) #returns 5

The reason for the "strange" syntax is that internally python translates len(object) into object.__len__(). This applies to any object. So, if you are defining some class and it makes sense for it to have a length, just define a __len__() method on it and then one can call len on those instances.