Collections.UserDict in Python

Difficulty Level : Easy
Last Updated : 26 Mar, 2020

An unordered collection of data value that is used to store data values like a map is known as Dictionary in Python. Unlike other Data Types that hold only single value as an element, Dictionary holds key:value pair. Key-value is provided in the dictionary to make it more optimized.

Note: For more information, refer to Python Dictionary

Collections.UserDict

Python supports a dictionary like a container called UserDict present in the collections module. This class acts as a wrapper class around the dictionary objects. This class is useful when one wants to create a dictionary 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 dictionary. This class takes a dictionary instance as an argument and simulates a dictionary that is kept in a regular dictionary. The dictionary is accessible by the data attribute of this class.

Syntax:

collections.UserDict([initialdata])

Example 1:

# Python program to demonstrate
# userdict
  
  
from collections import UserDict
  
  
d = {'a':1,
    'b': 2,
    'c': 3}
  
# Creating an UserDict
userD = UserDict(d)
print(userD.data)
  
  
# Creating an empty UserDict
userD = UserDict()
print(userD.data)

Output:

{'a': 1, 'b': 2, 'c': 3}
{}

Example 2: Let’s create a class inherting from UserDict to implement a customised dictionary.

# Python program to demonstrate
# userdict
   
  
from collections import UserDict
   
  
# Creating a Dictionary where
# deletion is not allowed
class MyDict(UserDict):
      
    # Function to stop deleltion
    # from dictionary
    def __del__(self):
        raise RuntimeError("Deletion not allowed")
          
    # Function to stop pop from 
    # dictionary
    def pop(self, s = None):
        raise RuntimeError("Deletion not allowed")
          
    # Function to stop popitem 
    # from Dictionary
    def popitem(self, s = None):
        raise RuntimeError("Deletion not allowed")
      
# Driver's code
d = MyDict({'a':1,
    'b': 2,
    'c': 3})
  
print("Original Dictionary")
print(d)
  
d.pop(1)

Output:

Original Dictionary
{'a': 1, 'c': 3, 'b': 2}

Traceback (most recent call last):
  File "/home/3ce2f334f5d25a3e24d10d567c705ce6.py", line 35, in 
    d.pop(1)
  File "/home/3ce2f334f5d25a3e24d10d567c705ce6.py", line 20, in pop
    raise RuntimeError("Deletion not allowed")
RuntimeError: Deletion not allowed
Exception ignored in: 
Traceback (most recent call last):
  File "/home/3ce2f334f5d25a3e24d10d567c705ce6.py", line 15, in __del__
RuntimeError: Deletion not allowed

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