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Python Dictionary

  • Difficulty Level : Easy
  • Last Updated : 15 Aug, 2021

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 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 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

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




# 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.

Python3




# 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.

Python3




# 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.

Python3




# 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: 
{}

Dictionary Methods 

MethodsDescription
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.

Recent Articles on Python Dictionary

https://youtu.be/z7z_e5

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