my_list = [1,2,3,4,5] len(my_list) # 5
The same works for tuples:
my_tuple = (1,2,3,4,5) len(my_tuple) # 5
And strings, which are really just arrays of characters:
my_string = 'hello world' len(my_string) # 11
It was intentionally done this way so that lists, tuples and other container types didn't all need to explicitly implement a public
.length() method, instead you can just check the
len() of anything that implements the 'magic'
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.
The functional nature of
len() also lends itself well to functional styles of programming.
lengths = map(len, list_of_containers)
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
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.