Table of Contents
In this tutorial, we will learn about the Python len() function with the help of examples.
The len()
function returns the number of items (length) in an object.
Example
languages = ['Python', 'Java', 'JavaScript'] # compute the length of languages length = len(languages) print(length) # Output: 3
1. len() Syntax
The syntax of len()
is:
len(s)
2. len() Parameters
The len()
function takes a single argument s, which can be
- sequence – string, bytes, tuple, list, range OR,
- collection – dictionary, set, frozen set
3. len() Return Value
len()
function returns the number of items of an object.
Failing to pass an argument or passing an invalid argument will raise a TypeError
exception.
4. Example 1: How len() works with tuples, lists and range?
testList = [] print(testList, 'length is', len(testList)) testList = [1, 2, 3] print(testList, 'length is', len(testList)) testTuple = (1, 2, 3) print(testTuple, 'length is', len(testTuple)) testRange = range(1, 10) print('Length of', testRange, 'is', len(testRange))
Output
[] length is 0 [1, 2, 3] length is 3 (1, 2, 3) length is 3 Length of range(1, 10) is 9
Visit these pages to learn more about:
- Python Lists
- Python Tuples
- Python range() Method
5. Example 2: How len() works with strings and bytes?
testString = '' print('Length of', testString, 'is', len(testString)) testString = 'Python' print('Length of', testString, 'is', len(testString)) # byte object testByte = b'Python' print('Length of', testByte, 'is', len(testByte)) testList = [1, 2, 3] # converting to bytes object testByte = bytes(testList) print('Length of', testByte, 'is', len(testByte))
Output
Length of is 0 Length of Python is 6 Length of b'Python' is 6 Length of b'\x01\x02\x03' is 3
Visit these pages to learn more about:
6. Example 3: How len() works with dictionaries and sets?
testSet = {1, 2, 3} print(testSet, 'length is', len(testSet)) # Empty Set testSet = set() print(testSet, 'length is', len(testSet)) testDict = {1: 'one', 2: 'two'} print(testDict, 'length is', len(testDict)) testDict = {} print(testDict, 'length is', len(testDict)) testSet = {1, 2} # frozenSet frozenTestSet = frozenset(testSet) print(frozenTestSet, 'length is', len(frozenTestSet))
Output
{1, 2, 3} length is 3 set() length is 0 {1: 'one', 2: 'two'} length is 2 {} length is 0 frozenset({1, 2}) length is 2
Visit these pages to learn more about:
- Python Dictionary
- Python Set
- Python frozenset()
Internally, len()
calls the object’s __len__
method. You can think of len()
as:
def len(s): return s.__len__()
So, you can assign custom length to the object (if necessary)
7. Example 4: How len() works for custom objects?
class Session: def __init__(self, number = 0): self.number = number def __len__(self): return self.number # default length is 0 s1 = Session() print(len(s1)) # giving custom length s2 = Session(6) print(len(s2))
Output
0 6
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