Python Dictionary
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] = 1print("\nDictionary after adding 3 elements: ") print(Dict) # Adding set of values # to a single Key Dict['Value_set'] = 2, 3, 4print("\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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