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Python Dictionary

  • Difficulty Level : Easy
  • Last Updated : 13 May, 2022

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. 
 

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




# 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


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