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Python collections.UserDict

The Python UserDict() is a dictionary present in the collections module. It is a class acts as a wrappers 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 adding new behavior to 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.

Following is the syntax of the Python UserDict()−

collection.UserDict([data])

It accepts dictionary as a parameter.

This class returns <class 'collections.UserDict'> object.

Following is a basic example of the Python Userdict() class −

from collections import UserDict
dic = {'a':1,'b': 2,'c': 3,'d':4}
# Creating an UserDict
userD = UserDict(dic)
print(userD)

Following is the output of the above code −

{'a': 1, 'b': 2, 'c': 3, 'd': 4}

We can inherit the properties of the Userdict() and we can add new functions into the class and can also modify the existing methods.

Here, we have create a class, MyDict and inherited the properties of Userdict class. Modified few methods and can added new methods −

# Python program to demonstrate
# userdict
from collections import UserDict
# Creating a Dictionary where
# deletion is not allowed
class MyDict(UserDict):
	# Function to stop deletion
	# 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
dict = MyDict({'a':1,'b': 2,'c': 3})
print("Original Dictionary :", dict)
dict.pop(1)

Following is the output of the above code −

Original Dictionary : {'a': 1, 'b': 2, 'c': 3}
Traceback (most recent call last):
  File "/home/cg/root/43843/main.py", line 30, in <module>
    dict.pop(1)
  File "/home/cg/root/43843/main.py", line 20, in pop
    raise RuntimeError("Deletion not allowed")
RuntimeError: Deletion not allowed
Exception ignored in: <function MyDict.__del__ at 0x7f2456043880>
Traceback (most recent call last):
  File "/home/cg/root/43843/main.py", line 15, in __del__
RuntimeError: Deletion not allowed

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