Dictionary in Python

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 single value as an element, Dictionary holds key:value pair. Key value is provided in the dictionary to make it more optimized and simpler.

Note – Keys in a dictionary doesn’t allows Polymorphism.

Polymorphism : 

Polymorphism is the ability of an object to take on many forms. The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object.

we will discuss about this topic in our upcoming Articles.

Creating a Dictionary

In Python, a Dictionary can be created by placing sequence of elements within curly {} braces, separated by ‘comma’, this is the syntax mainly, 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 –

The Dictionary keys are case sensitive, same name but different cases of Key will be treated distinctly.

# Creating a Dictionary 

# with Integer Keys

Dict = {1: 'Code', 2: 'For', 3: 'Job'}

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

print(Dict)

  

# Creating a Dictionary 

# with Mixed keys

Dict = {'Name': 'Code', 1: [1, 2, 3, 4, 5]}

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

print(Dict)

output :

Dictionary with the use of Integer Keys: 
{1: 'Code', 2: 'For', 3: 'Job'}

Dictionary with the use of Mixed Keys: 
{'Name': 'Code', 1: [1, 2, 3, 4, 5]}

Note - 

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: 'Code', 2: 'For', 3:'Job'})

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

print(Dict)

  

# Creating a Dictionary

# with each item as a Pair

Dict = dict([(1, 'Code'), (2, 'Dudle')])

print("\nDictionary with each item as a pair: ")

print(Dict)

output :

Empty Dictionary: 
{}

Dictionary with the use of dict() method : 
{1: 'Code', 2: 'For', 3: 'Job'}

Dictionary with each item as a pair: 
{1: 'Code', 2: 'Dudle'}

Nested Dictinary :

A Dictionary within the Dictionary by using of same curly braces in the curly braces

# Creating a Nested Dictionary 

# as shown in the below image

Dict = {1: 'Code', 2: 'For', 

        3:{'A' : 'Welcome', 'B' : 'To', 'C' : 'CodeDudle'}}

  

print(Dict) 

output :

{1: 'Code', 2: 'For', 3: {'A': 'Welcome', 'B': 'To', 'C': 'CodeDudle'}}

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.

Lets see by a code

# Creating an empty Dictionary

Dict = {}

print("Empty Dictionary: ")

print(Dict)

  

# Adding elements one at a time

Dict[0] = 'Code'

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' : 'Code'}}

print("\nAdding a Nested Key: ")

print(Dict)

output :

Empty Dictionary: 
{}

Dictionary after adding 3 elements: 
{0: 'Code', 2: 'For', 3: 1}

Dictionary after adding 3 elements: 
{0: 'Code', 2: 'For', 3: 1, 'Value_set': (2, 3, 4)}

Updated key value: 
{0: 'Code', 2: 'Welcome', 3: 1, 'Value_set': (2, 3, 4)}

Adding a Nested Key: 
{0: 'Code', 2: 'Welcome', 3: 1, 'Value_set': (2, 3, 4), 5: {'Nested': {'1': 'Life', '2': 'Code'}}}

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 to access the elements inside the dictionary.

# Python program to demonstrate  

# accessing a element from a Dictionary 

  

# Creating a Dictionary 

Dict = {1: 'Code', 'name': 'For', 3: 'Job'}

  

# 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:
Code

There is another method available for accessing the elements inside the dictionary called get().

# Creating a Dictionary 

Dict = {1: 'Code', 'name': 'For', 3: 'Job'}

  

# accessing a element using get()

# method

print("Accessing a element using get:")

print(Dict.get(3))

output :

Accessing a element using get:
Job

Accessing element of a nested dictionary

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

# Creating a Dictionary

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

        'Dict2': {'Name': 'For'}}

  

# Accessing element using key

print(Dict['Dict1'])

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

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

output :

{1: 'Code'}
Code
For

Removing Elements from Dictionary

Using del keyword

In Python Dictionary, deletion of a element perform 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.

# Initial Dictionary

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

        'A' : {1 : 'Code', 2 : 'For', 3 : 'Job'},

        'B' : {1 : 'dudle', 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: 
{5: 'Welcome', 6: 'To', 7: 'Code', 'A': {1: 'Code', 2: 'For', 3: 'Job'}, 'B': {1: 'dudle', 2: 'Life'}}

Deleting a specific key: 
{5: 'Welcome', 7: 'Code', 'A': {1: 'Code', 2: 'For', 3: 'Job'}, 'B': {1: 'dudle', 2: 'Life'}}

Deleting a key from Nested Dictionary: 
{5: 'Welcome', 7: 'Code', 'A': {1: 'Code', 3: 'Job'}, 'B': {1: 'dudle', 2: 'Life'}}

Using pop() method

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

# Creating a Dictionary

Dict = {1: 'Code', 'name': 'For', 3: 'Job'}

  

# 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: {'name': 'For', 3: 'Job'}
Value associated to poped key is: Code

Using popitem() method

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

# Creating Dictionary Dict = {1: 'Code', 'name': 'For', 3: 'Dudle'}    # 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: {1: 'Code', 'name': 'For'}
The arbitrary pair returned is: (3, 'Dudle')

Using clear() method

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

# Creating a Dictionary

Dict = {1: 'Code', 'name': 'For', 3: 'Dudle'}

  

  

# Deleting entire Dictionary

Dict.clear()

print("\nDeleting Entire Dictionary: ")

print(Dict)




output :




Deleting Entire Dictionary: 
{}

In this article i have describe about dictionary

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