Python – Add item after given Key in dictionary

Last Updated : 25 Apr, 2023

Given a dictionary and a Key, add new item after a particular key in dictionary.

Input : test_dict = {“Gfg” : 3, “is” : 5, “for” : 8, “Geeks” : 10}, K = “is”, add_item = {“good” : 19}
Output : {‘Gfg’: 3, ‘is’: 5, ‘good’: 19, ‘for’: 8, ‘Geeks’: 10}
Explanation : Item added after desired key in dictionary.

Input : test_dict = {“Gfg” : 3, “is” : 5, “for” : 8, “Geeks” : 10}, K = “for”, add_item = {“good” : 19}
Output : {‘Gfg’: 3, ‘is’: 5, ‘for’: 8, ‘good’: 19, ‘Geeks’: 10}
Explanation : Item added after desired key in dictionary.

Method 1: Using loop + update()

In this we iterate for all the keys, and when target key is encountered, the iteration is halted and dictionary is updated with required key. Then iteration is resumed.

Python3

# Python3 code to demonstrate working of 
# Dictionary Keys whose Values summation equals K 
# Using loop + update()
 
# initializing dictionary
test_dict = {"Gfg" : 3, "is" : 5, "for" : 8, "Geeks" : 10}
 
# printing original dictionary
print("The original dictionary is : " + str(test_dict))
 
# initializing K 
K = "is"
 
# initializing dictionary to be added 
add_item = {"best" : 19}
 
# using dictionary comprehension 
res = dict()
for key in test_dict:
    res[key] = test_dict[key]
     
    # modify after adding K key
    if key == K:
        res.update(add_item)
 
# printing result 
print("Modified dictionary : " + str(res)) 

Output

The original dictionary is : {'Gfg': 3, 'is': 5, 'for': 8, 'Geeks': 10}
Modified dictionary : {'Gfg': 3, 'is': 5, 'best': 19, 'for': 8, 'Geeks': 10}

Time Complexity: O(n), where n is the values in dictionary
Auxiliary Space: O(n), where n is the size of dictionary

Method 2: Using keys(),values(),items(),insert(),index() methods

Approach

Access the keys and values of test_dict using keys(),values()methods
Insert the new key into keys list and value into values list after K using insert(),index() method
Now create a new dictionary using keys list and values list by for loop
Display the new dictionary

Python3

# Python3 code to demonstrate working of
# Dictionary Keys whose Values summation equals K
 
# initializing dictionary
test_dict = {"Gfg" : 3, "is" : 5, "for" : 8, "Geeks" : 10}
 
# printing original dictionary
print("The original dictionary is : " + str(test_dict))
 
# initializing K
K = "is"
 
# initializing dictionary to be added
add_item = {"best" : 19}
res=dict()
a=list(add_item.items())
x=list(test_dict.keys())
y=list(test_dict.values())
x.insert(x.index(K)+1,a[0][0])
y.insert(x.index(K)+1,a[0][1])
for i in range(0,len(x)):
    res[x[i]]=y[i]
 
# printing result
print("Modified dictionary : " + str(res))

Output

The original dictionary is : {'Gfg': 3, 'is': 5, 'for': 8, 'Geeks': 10}
Modified dictionary : {'Gfg': 3, 'is': 5, 'best': 19, 'for': 8, 'Geeks': 10}

Time Complexity : O(N)
Auxiliary Space : O(N)

Method 3: Using dictionary comprehension and the get() method

Initialize the dictionary test_dict and the key K with their respective values.
Initialize the dictionary add_item with the key-value pair that needs to be added to the test_dict.
Calculate the sum of all values in the dictionary using the sum() method.
Check if the sum of all values is equal to K or not.
If the sum is equal to K, return the original dictionary as the result.
If the sum is not equal to K, add the new key-value pair to the dictionary and return the modified dictionary as the result.

Python3

# Python3 code to demonstrate working of
# Dictionary Keys whose Values summation equals K
# Using dictionary comprehension and get()
 
# initializing dictionary
test_dict = {"Gfg" : 3, "is" : 5, "for" : 8, "Geeks" : 10}
 
# printing original dictionary
print("The original dictionary is : " + str(test_dict))
 
# initializing K
K = 18
 
# initializing dictionary to be added
add_item = {"best" : 19}
 
# calculate the sum of all values in the dictionary
sum_values = sum(test_dict.values())
 
# check if the sum of all values is equal to K or not
if sum_values == K:
    res = test_dict
else:
    # add the new key-value pair to the dictionary
    test_dict.update(add_item)
 
    # return the modified dictionary
    res = test_dict
 
# printing result
print("Modified dictionary : " + str(res))

Output

The original dictionary is : {'Gfg': 3, 'is': 5, 'for': 8, 'Geeks': 10}
Modified dictionary : {'Gfg': 3, 'is': 5, 'for': 8, 'Geeks': 10, 'best': 19}

Time complexity: O(n), where n is the number of elements in the dictionary.
Auxiliary space: O(1), as we are not using any extra space for computation.