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 single value as an element, Dictionary holds key:value
pair. Key value is provided in the dictionary to make it more optimized. Each key-value pair in a Dictionary is separated by a colon :, whereas each key is separated by a ‘comma’.
A Dictionary in Python works similar to the Dictionary in a real world. Keys of a Dictionary must be unique and of immutable data type such as Strings, Integers and tuples, but the key-values can be repeated and be of any type.
Note – Keys in a dictionary doesn’t allows Polymorphism.
Creating a Dictionary
In Python, a Dictionary can be created by placing sequence of elements within curly {} braces, separated by ‘comma’. Dictionary holds a pair of values, one being the Key and the other corresponding pair element being its Key:value
. Values in a dictionary can be of any datatype and can be duplicated, whereas keys can’t be repeated and must be immutable.
Dictionary can also be created by the built-in function dict(). An empty dictionary can be created by just placing to curly braces{}.
Note – Dictionary keys are case sensitive, same name but different cases of Key will be treated distinctly.
# Creating an empty Dictionary Dict = {} print ( "Empty Dictionary: " ) print ( Dict ) # Creating a Dictionary # with Integer Keys Dict = { 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' } print ( "
Dictionary with the use of Integer Keys: " ) print ( Dict ) # Creating a Dictionary # with Mixed keys Dict = { 'Name' : 'Geeks' , 1 : [ 1 , 2 , 3 , 4 ]} print ( "
Dictionary with the use of Mixed Keys: " ) print ( Dict ) # Creating a Dictionary # with dict() method Dict = dict ({ 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' }) print ( "
Dictionary with the use of dict(): " ) print ( Dict ) # Creating a Dictionary # with each item as a Pair Dict = dict ([( 1 , 'Geeks' ), ( 2 , 'For' )]) print ( "
Dictionary with each item as a pair: " ) print ( Dict ) |
Output:
Empty Dictionary: {} 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 with the use of dict(): {1: 'Geeks', 2: 'For', 3: 'Geeks'} Dictionary with each item as a pair: {1: 'Geeks', 2: 'For'}
Nested Dictionary:
# 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, 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.
# 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 ( "
Dictionary after adding 3 elements: " ) print ( Dict ) # Adding set of values # to a single Key Dict [ 'Value_set' ] = 2 , 3 , 4 print ( "
Dictionary after adding 3 elements: " ) print ( Dict ) # Updating existing Key's Value Dict [ 2 ] = 'Welcome' print ( "
Updated key value: " ) print ( Dict ) # Adding Nested Key value to Dictionary Dict [ 5 ] = { 'Nested' :{ '1' : 'Life' , '2' : 'Geeks' }} print ( "
Adding 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.There is also a method called get() that will also help in acessing the element from a dictionary.
# Python program to demonstrate # accesing a element from a Dictionary # Creating a Dictionary Dict = { 1 : 'Geeks' , 'name' : 'For' , 3 : 'Geeks' } # accessing a element using key print ( "Acessing a element using key:" ) print ( Dict [ 'name' ]) # accessing a element using key print ( "Acessing a element using key:" ) print ( Dict [ 1 ]) # accessing a element using get() # method print ( "Acessing a element using get:" ) print ( Dict .get( 3 )) |
Output:
Acessing a element using key: For Acessing a element using key: Geeks Acessing a element using get: Geeks
Removing Elements from Dictionary
In Python Dictionary, deletion of keys can be done by using the del
keyword. Using del keyword, specific values from a dictionary as well as whole dictionary can be deleted. Other functions like pop()
and popitem()
can also be used for deleting specific values and arbitrary values from a Dictionary. All the items from a dictionary can be deleted at once by using clear()
method. Items in a Nested dictionary can also be deleted by using del keyword and providing specific nested key and particular key to be deleted from that nested Dictionary.
Note- del Dict
will delete the entire dictionary and hence printing it after deletion will raise an Error.
# Initial Dictionary Dict = { 5 : 'Welcome' , 6 : 'To' , 7 : 'Geeks' , 'A' : { 1 : 'Geeks' , 2 : 'For' , 3 : 'Geeks' }, 'B' : { 1 : 'Geeks' , 2 : 'Life' }} print ( "Initial Dictionary: " ) print ( Dict ) # Deleting a Key value del Dict [ 6 ] print ( "
Deleting a specific key: " ) print ( Dict ) # Deleting a Key from # Nested Dictionary del Dict [ 'A' ][ 2 ] print ( "
Deleting a key from Nested Dictionary: " ) print ( Dict ) # Deleting a Key # using pop() Dict .pop( 5 ) print ( "
Popping specific element: " ) print ( Dict ) # Deleting a Key # using popitem() Dict .popitem() print ( "
Pops first element: " ) print ( Dict ) # Deleting entire Dictionary Dict .clear() print ( "
Deleting Entire 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'} Popping specific element: {'A': {1: 'Geeks', 3: 'Geeks'}, 'B': {1: 'Geeks', 2: 'Life'}, 7: 'Geeks'} Pops first element: {'B': {1: 'Geeks', 2: 'Life'}, 7: 'Geeks'} 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. |
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