Python Dictionary
Dictionary in Python is an unordered collection of data values, used to store data values like a map, which, unlike other Data Types that hold only a single value as an element, Dictionary holds key:value pair. Key-value is provided in the dictionary to make it more optimized.
Creating a Dictionary
In Python, a Dictionary can be created by placing a sequence of elements within curly {} braces, separated by ‘comma’. Dictionary holds pairs of values, one being the Key and the other corresponding pair element being its Key:value. Values in a dictionary can be of any data type and can be duplicated, whereas keys can’t be repeated and must be immutable.
Note – Dictionary keys are case sensitive, the same name but different cases of Key will be treated distinctly.
Python3
# Creating a Dictionary # with Integer Keys Dict = { 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' } print ( "\nDictionary with the use of Integer Keys: " ) print ( Dict ) # Creating a Dictionary # with Mixed keys Dict = { 'Name' : 'Geeks' , 1 : [ 1 , 2 , 3 , 4 ]} print ( "\nDictionary with the use of Mixed Keys: " ) print ( Dict ) |
Output:
Dictionary with the use of Integer Keys: {1: 'Geeks', 2: 'For', 3: 'Geeks'} Dictionary with the use of Mixed Keys: {1: [1, 2, 3, 4], 'Name': 'Geeks'}
Dictionary can also be created by the built-in function dict(). An empty dictionary can be created by just placing to curly braces{}.
Python3
# Creating an empty Dictionary Dict = {} print ( "Empty Dictionary: " ) print ( Dict ) # Creating a Dictionary # with dict() method Dict = dict ({ 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' }) print ( "\nDictionary with the use of dict(): " ) print ( Dict ) # Creating a Dictionary # with each item as a Pair Dict = dict ([( 1 , 'Geeks' ), ( 2 , 'For' )]) print ( "\nDictionary with each item as a pair: " ) print ( Dict ) |
Output:
Empty Dictionary: {} Dictionary with the use of dict(): {1: 'Geeks', 2: 'For', 3: 'Geeks'} Dictionary with each item as a pair: {1: 'Geeks', 2: 'For'}
Nested Dictionary:
Python3
# Creating a Nested Dictionary # as shown in the below image Dict = { 1 : 'Geeks' , 2 : 'For' , 3 :{ 'A' : 'Welcome' , 'B' : 'To' , 'C' : 'Geeks' }} print ( Dict ) |
Output:
{1: 'Geeks', 2: 'For', 3: {'A': 'Welcome', 'B': 'To', 'C': 'Geeks'}}
Adding elements to a Dictionary
In Python Dictionary, the Addition of elements can be done in multiple ways. One value at a time can be added to a Dictionary by defining value along with the key e.g. Dict[Key] = ‘Value’. Updating an existing value in a Dictionary can be done by using the built-in update() method. Nested key values can also be added to an existing Dictionary.
Note- While adding a value, if the key-value already exists, the value gets updated otherwise a new Key with the value is added to the Dictionary.
Python3
# Creating an empty Dictionary Dict = {} print ( "Empty Dictionary: " ) print ( Dict ) # Adding elements one at a time Dict [ 0 ] = 'Geeks' Dict [ 2 ] = 'For' Dict [ 3 ] = 1 print ( "\nDictionary after adding 3 elements: " ) print ( Dict ) # Adding set of values # to a single Key Dict [ 'Value_set' ] = 2 , 3 , 4 print ( "\nDictionary after adding 3 elements: " ) print ( Dict ) # Updating existing Key's Value Dict [ 2 ] = 'Welcome' print ( "\nUpdated key value: " ) print ( Dict ) # Adding Nested Key value to Dictionary Dict [ 5 ] = { 'Nested' :{ '1' : 'Life' , '2' : 'Geeks' }} print ( "\nAdding a Nested Key: " ) print ( Dict ) |
Output:
Empty Dictionary: {} Dictionary after adding 3 elements: {0: 'Geeks', 2: 'For', 3: 1} Dictionary after adding 3 elements: {0: 'Geeks', 2: 'For', 3: 1, 'Value_set': (2, 3, 4)} Updated key value: {0: 'Geeks', 2: 'Welcome', 3: 1, 'Value_set': (2, 3, 4)} Adding a Nested Key: {0: 'Geeks', 2: 'Welcome', 3: 1, 5: {'Nested': {'1': 'Life', '2': 'Geeks'}}, 'Value_set': (2, 3, 4)}
Accessing elements from a Dictionary
In order to access the items of a dictionary refer to its key name. Key can be used inside square brackets.
Python3
# Python program to demonstrate # accessing a element from a Dictionary # Creating a Dictionary Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' } # accessing a element using key print ( "Accessing a element using key:" ) print ( Dict [ 'name' ]) # accessing a element using key print ( "Accessing a element using key:" ) print ( Dict [ 1 ]) |
Output:
Accessing a element using key: For Accessing a element using key: Geeks
There is also a method called get() that will also help in accessing the element from a dictionary.
Python3
# Creating a Dictionary Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' } # accessing a element using get() # method print ( "Accessing a element using get:" ) print ( Dict .get( 3 )) |
Output:
Accessing a element using get: Geeks
Accessing an element of a nested dictionary
In order to access the value of any key in the nested dictionary, use indexing [] syntax.
Python3
# Creating a Dictionary Dict = { 'Dict1' : { 1 : 'Geeks' }, 'Dict2' : { 'Name' : 'For' }} # Accessing element using key print ( Dict [ 'Dict1' ]) print ( Dict [ 'Dict1' ][ 1 ]) print ( Dict [ 'Dict2' ][ 'Name' ]) |
Output:
{1: 'Geeks'}
Geeks
For