Cara menggunakan length of object python

The built-in

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

Lists, sets, dictionaries, strings, and most data structures in Python have a length:

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> len(numbers)
7

But numbers don't:

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

When making a class in Python, you can control whether instances of that class have a length.

Python's built-in

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

So if that object has a

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

If it doesn't have a

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

How to make instances of your class have a length?

Python's

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

>>> import random
>>> colors = ['red', 'blue', 'green', 'purple']
>>> random.choice(colors)
'purple'

This

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

Here we have a class named

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

class ForgivingIndexer:

    def __init__(self, sequence):
        self.sequence = sequence

    def __getitem__(self, index):
        return self.sequence[int(index)]

This class has a

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

But this isn't quite enough to allow our

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> import random
>>> fruits = ForgivingIndexer(['apple', 'lime', 'pear', 'watermelon'])
>>> random.choice(fruits)
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/lib/python3.10/random.py", line 378, in choice
    return seq[self._randbelow(len(seq))]
TypeError: object of type 'ForgivingIndexer' has no len()

Python gives us an error because

>>> numbers = [2, 1, 3, 4, 7, 11, 18]
>>> numbers.__len__()
7

Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> fruits = ForgivingIndexer(['apple', 'lime', 'pear', 'watermelon'])
>>> len(fruits)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'ForgivingIndexer' has no len()

In order to support the built-in

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

    def __len__(self):
        return len(self.sequence)

Now instances of this class have a length:

>>> import random
>>> fruits = ForgivingIndexer(['apple', 'lime', 'pear', 'watermelon'])
>>> len(fruits)
4

And they also work with

Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

Summary

You can make your objects work with the built-in

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()

>>> n = 10
>>> len(n)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: object of type 'int' has no len()