How To Create Dictionary In Dictionary Python

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.

Note – Keys in a dictionary don't allow Polymorphism.

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Disclamer: It is important to note that Dictionaries have been modified to maintain insertion order with the release of Python 3.7, so they are now ordered collection of data values.

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

Dict = { 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' }

print ( "\nDictionary with the use of Integer Keys: " )

print ( Dict )

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

Dict = {}

print ( "Empty Dictionary: " )

print ( Dict )

Dict = dict ({ 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' })

print ( "\nDictionary with the use of dict(): " )

print ( Dict )

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

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

Dict = {}

print ( "Empty Dictionary: " )

print ( Dict )

Dict [ 0 ] = 'Geeks'

Dict [ 2 ] = 'For'

Dict [ 3 ] = 1

print ( "\nDictionary after adding 3 elements: " )

print ( Dict )

Dict [ 'Value_set' ] = 2 , 3 , 4

print ( "\nDictionary after adding 3 elements: " )

print ( Dict )

Dict [ 2 ] = 'Welcome'

print ( "\nUpdated key value: " )

print ( Dict )

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

Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' }

print ( "Accessing a element using key:" )

print ( Dict [ 'name' ])

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

Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' }

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

Dict = { 'Dict1' : { 1 : 'Geeks' },

'Dict2' : { 'Name' : 'For' }}

print ( Dict [ 'Dict1' ])

print ( Dict [ 'Dict1' ][ 1 ])

print ( Dict [ 'Dict2' ][ 'Name' ])

Output:

{1: 'Geeks'} Geeks For

Removing Elements from Dictionary

Using del keyword

In Python Dictionary, deletion of keys can be done by using the del keyword. Using the del keyword, specific values from a dictionary as well as the whole dictionary can be deleted. Items in a Nested dictionary can also be deleted by using the del keyword and providing a specific nested key and particular key to be deleted from that nested Dictionary.

Note: The del Dict will delete the entire dictionary and hence printing it after deletion will raise an Error.

Python3

Dict = { 5 : 'Welcome' , 6 : 'To' , 7 : 'Geeks' ,

'A' : { 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' },

'B' : { 1 : 'Geeks' , 2 : 'Life' }}

print ( "Initial Dictionary: " )

print ( Dict )

del Dict [ 6 ]

print ( "\nDeleting a specific key: " )

print ( Dict )

del Dict [ 'A' ][ 2 ]

print ( "\nDeleting a key from Nested Dictionary: " )

print ( Dict )

Output:

Initial Dictionary:  {'A': {1: 'Geeks', 2: 'For', 3: 'Geeks'}, 'B': {1: 'Geeks', 2: 'Life'}, 5: 'Welcome', 6: 'To', 7: 'Geeks'}  Deleting a specific key:  {'A': {1: 'Geeks', 2: 'For', 3: 'Geeks'}, 'B': {1: 'Geeks', 2: 'Life'}, 5: 'Welcome', 7: 'Geeks'}  Deleting a key from Nested Dictionary:  {'A': {1: 'Geeks', 3: 'Geeks'}, 'B': {1: 'Geeks', 2: 'Life'}, 5: 'Welcome', 7: 'Geeks'}

Using pop() method

Pop() method is used to return and delete the value of the key specified.

Python3

Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' }

pop_ele = Dict .pop( 1 )

print ( '\nDictionary after deletion: ' + str ( Dict ))

print ( 'Value associated to poped key is: ' + str (pop_ele))

Output:

Dictionary after deletion: {3: 'Geeks', 'name': 'For'} Value associated to poped key is: Geeks

Using popitem() method

The popitem() returns and removes an arbitrary element (key, value) pair from the dictionary.

Python3

Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' }

pop_ele = Dict .popitem()

print ( "\nDictionary after deletion: " + str ( Dict ))

print ( "The arbitrary pair returned is: " + str (pop_ele))

Output:

Dictionary after deletion: {3: 'Geeks', 'name': 'For'} The arbitrary pair returned is: (1, 'Geeks')

Using clear() method

All the items from a dictionary can be deleted at once by using clear() method.

Python3

Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' }

Dict .clear()

print ( "\nDeleting Entire Dictionary: " )

print ( Dict )

Output:

Deleting Entire Dictionary:  {}

Dictionary Methods

Methods	Description
copy()	They copy() method returns a shallow copy of the dictionary.
clear()	The clear() method removes all items from the dictionary.
pop()	Removes and returns an element from a dictionary having the given key.
popitem()	Removes the arbitrary key-value pair from the dictionary and returns it as tuple.
get()	It is a conventional method to access a value for a key.
dictionary_name.values()	returns a list of all the values available in a given dictionary.
str()	Produces a printable string representation of a dictionary.
update()	Adds dictionary dict2's key-values pairs to dict
setdefault()	Set dict[key]=default if key is not already in dict
keys()	Returns list of dictionary dict's keys
items()	Returns a list of dict's (key, value) tuple pairs
has_key()	Returns true if key in dictionary dict, false otherwise
fromkeys()	Create a new dictionary with keys from seq and values set to value.
type()	Returns the type of the passed variable.
cmp()	Compares elements of both dict.