Python Len() - Programiz

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The len() function returns the length (the number of items) of an object.

Example

languages = ['Python', 'Java', 'JavaScript'] length = len(languages) print(length) # Output: 3

len() Syntax

The syntax of len() is:

len(s)

len() Argument

The len() function takes a single object as argument. It can be:

  • Sequence - list, tuple, string, range, etc.
  • Collection - set, dictionary etc.

len() Return Value

It returns an integer (the length of the object).

Example 1: Working of len() with Tuples, Lists and Range

x = [1, 2, 3] print(len(x)) # Output: 3 y = (1, 2, 3) print(len(y)) # Output: 3 z = range(8, 20, 3) print(len(z)) # Output: 4

Visit these pages to learn more about:

  • Python range()
  • Python Lists
  • Python Tuples

Example 2: len() with Strings, Dictionaries and Sets

text = 'Python' print(len(text)) # Output: 6 person = {"name": 'Amanda', "age": 21} print(len(person)) # Output: 2 animals = {'tiger', 'lion', 'tiger', 'cat'} print(len(animals)) # Output: 3

Visit these pages to learn more about:

  • Python Strings
  • Python Dictionaries
  • Python Sets

len() with User-defined Objects

The len() function internally calls the object's __len__() method. You can think of len() as:

def len(s): return s.__len__()

Therefore, we can make len() work for a user-defined object by implementing the ___len___() method.

Example 3: len() with User-defined Object

class Session: def __init__(self, number = 0): self.number = number def __len__(self): return self.number # default length is 0 session1 = Session() print(len(session1)) # Output: 0 session2 = Session(6) print(len(session2)) # Output: 6

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