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Python program to insert an element at the beginning in OrderedDict

Here, we will see a Python program to insert an element entered by the user at the beginning in OrderedDict.
Submitted by Shivang Yadav, on May 22, 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 } 

Ordered Dictionary is a special type of dictionary which remembers the order of insertion of keys.

Inserting at the beginning of OrderedDict

We have an OrderedDict in Python and a key-value pair which is entered by the user. We need to add it to the beginning of the OrderedDict.

Input: 
orderedDict = {'javascript' : 4, 'python' : 7, 'c' : 4} -> 'r' : 5

Output: 
{'r' : 5, 'javascript' : 4, 'python' : 7, 'c' : 4}

Python provides multiple methods to insert an element to the beginning of the OrderedDict.

Let's see some methods...

Method 1:

A simple approach is by creating a new OrderedDict from the entered key value pair and then creating a new one by merging them in such a way that the entered pair comes at the beginning of this OrderedDict.

Program to insert an element at the beginning in OrderedDict

# Python program to insert an element at the beginning in OrderedDict
from collections import OrderedDict

# creating a OrderedDict
myDict = OrderedDict([('javascript', '4'), ('python', '12')])
print("Original dictionary : ", str(myDict))

print("Enter the key-value pair to be added in the OrderedDict")
key = input("key : ")
value = input("value : ")
addedDict = OrderedDict([(key, value)])

# Inserting key-value pair at the beginning of the OrderedDict 
newOrderedDict = OrderedDict(list(addedDict.items()) + list(myDict.items()))

# Printing the Resultant dictionary
print ("Resultant Dictionary :"+str(newOrderedDict))

Output:

riginal dictionary :  OrderedDict([('javascript', '4'), ('python', '12')])
Enter the key-value pair to be added in the OrderedDict
key : r
value : 1
Resultant Dictionary :OrderedDict([('r', '1'), ('javascript', '4'), ('python', '12')])

Method 2: Using Python's built-in method

Python provides a built-in method to add a key-value pair to the orderedDict using update() method and then move the pair to the beginning of the orderedDict using move_to_end() method.

Program to insert an element at the beginning in OrderedDict

# Python program to insert an element at the beginning in OrderedDict
from collections import OrderedDict

# creating a OrderedDict
myDict = OrderedDict([('javascript', '4'), ('python', '12')])
print("Original dictionary : ", str(myDict))

print("Enter the key-value pair to be added in the OrderedDict")
key = input("key : ")
value = input("value : ")
addedDict = OrderedDict([(key, value)])

# Inserting key-value pair at the beginning of the OrderedDict 
myDict.update({key:value})
myDict.move_to_end(key, last = False)

# Printing the Resultant dictionary
print ("Resultant Dictionary : "+str(myDict))

Output:

Original dictionary :  OrderedDict([('javascript', '4'), ('python', '12')])
Enter the key-value pair to be added in the OrderedDict
key : r
value : 1
Resultant Dictionary : OrderedDict([('r', '1'), ('javascript', '4'), ('python', '12')])

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