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The len() function counts the number of items in an object.
Its syntax is as follows:
1 | len(obj) -> length |
| Parameter | Description |
|---|---|
| obj | obj can be a string, list, dictionary, tuple etc. |
Here is an example:
1 2 3 4 5 6 7 8 9 10 11 12 13 | >>> >>> len([1, 2, 3, 4, 5]) # length of list 5 >>> >>> len({"spande", "club", "diamond", "heart"}) # length of set 4 >>> >>> len(("alpha", "beta", "gamma")) # length of tuple 3 >>> >>> len({ "mango": 10, "apple": 40, "plum": 16 }) # length of dictionary 3 >>> |
Ironically, the len() function doesn’t work with a generator. Trying to call len() on a generator object will result in TypeError exception.
1 2 3 4 5 6 7 8 9 10 11 12 | >>> >>> def gen_func(): ... for i in range(5): ... yield i ... >>> >>> >>> len(gen_func()) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: object of type 'generator' has no len() >>> |
len() with User defined objects
To use len() on user-defined objects you will have to implement the __len__() method.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | >>> >>> class Stack: ... ... def __init__(self): ... self._stack = [] ... ... def push(self, item): ... self._stack.append(item) ... ... def pop(self): ... self._stack.pop() ... ... def __len__(self): ... return len(self._stack) ... >>> >>> s = Stack() >>> >>> len(s) 0 >>> >>> s.push(2) >>> s.push(5) >>> s.push(9) >>> s.push(12) >>> >>> len(s) 4 >>> |
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