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OrderedDict in Python

Python | OrderedDict: Here, we will learn about the OrderedDict with examples in Python programming language.
Submitted by Shivang Yadav, on May 27, 2021

Python programming language is a high-level and object-oriented programming language. Python is an easy to learn, powerful high-level programming language. It has a simple but effective approach to object-oriented programming.

Dictionary is a collection in python which is used to store data as Key:value pair.

Example:

dict = { "python" : 1, "C++" : 3, "javaScript" : 2 } 

OrderedDict

OrderedDict is a special type of dictionary in Python in which the order of insertion of key-value pairs is preserved. 

The OrderedDict collection is imported in Python from the collections library as OrderedDict. 

Import syntax:

from collections import OrderedDict

Syntax for creating a new OrderedDict

OrderedDict_Name = OrderedDict([(key1, value1), (key2, value2), ...])

Python Program to create an OrderedDict

# Python program to create an OrderedDict 
from collections import OrderedDict

# Creating a OrderedDict
myOrderedDict = OrderedDict([('javascript', '4'), ('python', '12'), ('R', '7')])

# Printing 
print("Ordered dictionary : ", str(myOrderedDict))

Output:

Ordered dictionary :  OrderedDict([('javascript', '4'), ('python', '12'), ('R', '7')])

Difference b/w Regular Dictionary and Ordered Dictionary

There is a major difference between a regular dictionary and OrderedDict in the order of insertion. It is the fact that there is no order of insertion present in a regular dictionary but in the case of OrderedDict, the order in which the key-value pairs are inserted remains the same.

Let's a program which compares both types of dictionaries...

# Python program for difference b/w 
# regular dictionary and Ordered dictionary

from collections import OrderedDict

# Creating a regular dictionary
myDict = {'javascript': 4, 'python': 12, 'R':7 }
print("Regular dictionary : ", str(myDict))

# Creating a OrderedDict
myOrderedDict = OrderedDict([('javascript', 4), ('python', 12), ('R', 7)])
print("Ordered dictionary : ", str(myOrderedDict))

Output:

Regular dictionary :  {'R': 7, 'javascript': 4, 'python': 12}
Ordered dictionary :  OrderedDict([('javascript', 4), ('python', 12), ('R', 7)])

Effect of changing values on the order of OrderedDict

If we change the value of a key-value pair of an OrderedDict, the order will remain the same after the change.

Python program to illustrate the concept

# Python program for difference b/w 
# regular dictionary and Ordered dictionary

from collections import OrderedDict

# Creating a OrderedDict
myOrderedDict = OrderedDict([('javascript', 4), ('python', 12), ('R', 7)])
print("Ordered dictionary : ", str(myOrderedDict))

# Changing the value of a key-value pair
myOrderedDict['python'] = 1

# printing values 
print("Updated Ordered dictionary : ", str(myOrderedDict))

Output:

Ordered dictionary :  OrderedDict([('javascript', 4), ('python', 12), ('R', 7)])
Updated Ordered dictionary :  OrderedDict([('javascript', 4), ('python', 1), ('R', 7)])