Collections.UserList in Python
Python Lists are array-like data structure but unlike it can be homogeneous. 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:
Python3
# Python program to demonstrate# userlistfrom collections import UserListL = [1, 2, 3, 4]# Creating a userlistuserL = UserList(L)print(userL.data)# Creating empty userlistuserL = UserList()print(userL.data) |
Output:
[1, 2, 3, 4] []
Example 2:
Python3
# Python program to demonstrate# userlist from collections import UserList # Creating a List where# deletion is not allowedclass MyList(UserList): # Function to stop deletion # 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 codeL = MyList([1, 2, 3, 4])print("Original List")# Inserting to List"L.append(5)print("After Insertion")print(L)# Deleting From ListL.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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