Python dictionaries are powerful data structures that allow you to store and retrieve data using key-value pairs. Appending an item to a list within a dictionary involves accessing the list by its corresponding key and then using the append() method to add the new item to the list in Python.
Example
Input: {'Destination': 'China', 'Nationality': 'Italian', 'Age': [20]}
Output: {'Destination': 'China', 'Nationality': 'Italian', 'Age': [20, 'Twenty']}
Explaination: Appended "Twenty" in the list of keys of Age.
How to Append into a List in Dictionary
In Python, we can append to a list in a dictionary in several ways, we are explaining some generally used methods which are used for appending to a list in Python Dictionary.
- Using += Operator
- Using List append() Method
- Using defaultdict() Method
- Using update() Function
- Using dict() Method
- Using extend() Method
- Using List Comprehension
Append to a List in Dictionary using += Operator
In this method, we will use the “+=” operator to append a Python list into the dictionary, for this we will take a dictionary and then add elements as a list into the dictionary.
Example: In this example, the below code initializes a dictionary ‘Details’ with key-value pairs. It then appends the list [20, “Twenty”] to the ‘Age’ key in the dictionary and prints the original and modified versions of ‘Details’.
Python3
Details = { "Destination" : "China" ,
"Nationality" : "Italian" , "Age" : []}
print ( "Original:" , Details)
Details[ "Age" ] + = [ 20 , "Twenty" ]
print ( "Modified:" , Details)
|
Output:
Original: {'Destination': 'China', 'Nationality': 'Italian', 'Age': []}
Modified: {'Destination': 'China', 'Nationality': 'Italian', 'Age': [20, 'Twenty']}
Appending a Dictionary to a List in Python using the List append() Method
In this method, we will use conditions for checking the key and then append to a dictionary list using the list append() method.
Example: In this example, the below code creates a dictionary named “Details” and, if “Age” is a key, appends “Twenty” to the corresponding list, printing the modified dictionary.
Python3
Details = { "Destination" : "China" ,
"Nationality" : "Italian" , "Age" : [ 20 ]}
print ( "Original:" , Details)
if "Age" in Details:
Details[ "Age" ].append( "Twenty" )
print ( "Modified:" , Details)
|
Output:
Original: {'Destination': 'China', 'Nationality': 'Italian', 'Age': [20]}
Modified: {'Destination': 'China', 'Nationality': 'Italian', 'Age': [20, 'Twenty']}
Append a dictionary to a list in Python using defaultdict() Method
In this method, we are using the defaultdict() function. It is a part of the collections module. We have to import the function from the collections module to use it in the program and then use it to append to a dictionary list. Since append takes only one parameter, to insert another parameter, repeat the append method.
Example: In this example, the below code uses a defaultdict() to create a dictionary called “Details” with default values as empty lists. It then appends “India” and “Pakistan” to the “Country” key’s list, showcasing the modified dictionary.
Python3
from collections import defaultdict
Details = defaultdict( list )
print ( "Original:" , Details)
Details[ "Country" ].append( "India" )
Details[ "Country" ].append( "Pakistan" )
print ( "Modified:" , Details)
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Output:
Original: defaultdict(<class 'list'>, {})
Modified: defaultdict(<class 'list'>, {'Country': ['India', 'Pakistan']})
Python Append to a List in Dictionary using update() Function
We will use the Python dictionary update() function to add a new list to the dictionary. We can use the update() function to embed a dictionary inside another dictionary.
Example: In this example below code initializes a dictionary with destination and nationality, adds an empty list to the “Age” key, prints the original dictionary, and updates “Age” with a list of ages using `update()`, resulting in a modified dictionary.
Python3
Details = { "Destination" : "China" ,
"Nationality" : "Italian" }
Details[ "Age" ] = []
print ( "Original:" , Details)
Details.update({ "Age" : [ 18 , 20 , 25 , 29 , 30 ]})
print ( "Modified:" , Details)
|
Output:
Original: {'Destination': 'China', 'Nationality': 'Italian', 'Age': []}
Modified: {'Destination': 'China', 'Nationality': 'Italian', 'Age': [18, 20, 25, 29, 30]}
Append to a Dictionary in Python using dict() function
You can convert a list into a value for a key in a Python dictionary using dict() function.
Example: In this example below code creates a dictionary named “Details” with the key “Age” and values from the list [18, 20, 25, 29, 30], then prints the resulting dictionary.
Python3
Values = [ 18 , 20 , 25 , 29 , 30 ]
Details = dict ({ "Age" : Values})
print (Details)
|
Output:
{'Age': [18, 20, 25, 29, 30]}
Appending to a List in a Dictionary using extend() Method
The extend() method is used to append elements from an iterable, such as a list, to the end of another list. It modifies the original iterable in place by adding elements from the provided iterable.
Example : In this example below code initializes a dictionary “Details” with a key “Age” and values as a list. It then extends the list with additional values [35, 40] and prints the modified dictionary.
Python3
Details = { "Age" : [ 18 , 20 , 25 , 29 , 30 ]}
Details[ "Age" ].extend([ 35 , 40 ])
print (Details)
|
Output :
{'Age': [18, 20, 25, 29, 30, 35, 40]}
Append Values to List in Dictionary using List Comprehension
Appending values to a list within a Python dictionary, using list comprehension involves creating a new list by iterating over existing elements and adding the desired values.
Example: In this example, the list comprehension [x for x in Details[“Age”]] iterates over each element in the existing “Age” list. Then, the list is extended by adding the values from the extra_values list.
Python3
Details = { "Age" : [ 18 , 20 , 25 , 29 , 30 ]}
extra_values = [ 35 , 40 ]
Details[ "Age" ] = [x for x in Details[ "Age" ]] + extra_values
print (Details)
|
Output :
{'Age': [18, 20, 25, 29, 30, 35, 40]}
We have covered various ways of appending a list in the dictionary in Python. You can easily add values to a list in the dictionary. This makes it much easier to integrate iterables into each other and update them individually according to needs.
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Last Updated :
20 Dec, 2023
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