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Collections.UserList in Python
  • Last Updated : 26 Mar, 2020
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Python Lists are array-like data structure but unlike it can be homogenous. A single list may contain DataTypes like Integers, Strings, as well as Objects. List in Python are ordered and have a definite count. The elements in a list are indexed according to a definite sequence and the indexing of a list is done with 0 being the first index.

Note: For more information, refer to Python List

Collections.UserList

Python supports a List like a container called UserList present in the collections module. This class acts as a wrapper class around the List objects. This class is useful when one wants to create a list of their own with some modified functionality or with some new functionality. It can be considered as a way of adding new behaviors for the list. This class takes a list instance as an argument and simulates a list that is kept in a regular list. The list is accessible by the data attribute of the this class.

Syntax:

collections.UserList([list])

Example 1:






# Python program to demonstrate
# userlist
  
  
from collections import UserList
  
  
L = [1, 2, 3, 4]
  
# Creating a userlist
userL = UserList(L)
print(userL.data)
  
  
# Creating empty userlist
userL = UserList()
print(userL.data)

Output:

[1, 2, 3, 4]
[]

Example 2:




# Python program to demonstrate
# userlist
   
  
from collections import UserList
   
  
# Creating a List where
# deletion is not allowed
class MyList(UserList):
      
    # Function to stop deleltion
    # from List
    def remove(self, s = None):
        raise RuntimeError("Deletion not allowed")
          
    # Function to stop pop from 
    # List
    def pop(self, s = None):
        raise RuntimeError("Deletion not allowed")
      
# Driver's code
L = MyList([1, 2, 3, 4])
  
print("Original List")
  
# Inserting to List"
L.append(5)
print("After Insertion")
print(L)
  
# Deliting From List
L.remove()

Output:

Original List
After Insertion
[1, 2, 3, 4, 5]
Traceback (most recent call last):
  File "/home/9399c9e865a7493dce58e88571472d23.py", line 33, in 
    L.remove()
  File "/home/9399c9e865a7493dce58e88571472d23.py", line 15, in remove
    raise RuntimeError("Deletion not allowed")
RuntimeError: Deletion not allowed

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