Python Dictionary

Python Dictionary

Dictionary in Python is an ordered 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 optimised.
Note – Keys in a dictionary don’t allow Polymorphism.

Disclaimer: 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 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.
Note – Dictionary keys are case sensitive, same name but different cases of Key will be treated distinctly.

# 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{}.

# 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:

 

 

# 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("\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.

# 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 acessing the element from a dictionary.

# 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 element of a nested dictionary

In order to access the value of any key in nested dictionary, use indexing [] syntax.

# 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

 

Removing Elements from Dictionary

 

Using del keyword

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. 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("\nDeleting a specific key: ")
print(Dict)
# Deleting a Key from
# Nested Dictionary
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.

# Creating a Dictionary
Dict = {1: 'Geeks', 'name': 'For', 3: 'Geeks'}
# Deleting a key
# using pop() method
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.

# Creating Dictionary
Dict = {1: 'Geeks', 'name': 'For', 3: 'Geeks'}
# Deleting an arbitrary key
# using popitem() function
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.



# Creating a Dictionary
Dict = {1: 'Geeks', 'name': 'For', 3: 'Geeks'}
# Deleting entire Dictionary
Dict.clear()
print("\nDeleting Entire Dictionary: ")
print(Dict)

Output:

Deleting Entire Dictionary: 
{}