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 single value as an element, Dictionary holds key:value pair. Key value is provided in the dictionary to make it more optimized. Each key-value pair in a Dictionary is separated by a colon :, whereas each key is separated by a ‘comma’.
A Dictionary in Python works similar to the Dictionary in a real world. Keys of a Dictionary must be unique and of immutable data type such as Strings, Integers and tuples, but the key-values can be repeated and be of any type.
Note – Keys in a dictionary doesn’t allows Polymorphism.
Creating a Dictionary
In Python, a Dictionary can be created by placing 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.
Dictionary can also be created by the built-in function dict(). An empty dictionary can be created by just placing to curly braces{}.
Note – Dictionary keys are case sensitive, same name but different cases of Key will be treated distinctly.
# Creating an empty Dictionary Dict = {} print("Empty Dictionary: ") print(Dict) # 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) # 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) |
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Output:
Empty Dictionary:
{}
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 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) |
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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] = 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) |
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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.There is also a method called get() that will also help in acessing the element from a dictionary.
# Python program to demonstrate # accesing a element from a Dictionary # Creating a Dictionary Dict = {1: 'Geeks', 'name': 'For', 3: 'Geeks'} # accessing a element using key print("Acessing a element using key:") print(Dict['name']) # accessing a element using key print("Acessing a element using key:") print(Dict[1]) # accessing a element using get() # method print("Acessing a element using get:") print(Dict.get(3)) |
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Output:
Acessing a element using key: For Acessing a element using key: Geeks Acessing a element using get: Geeks
Removing Elements from Dictionary
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. Other functions like pop() and popitem() can also be used for deleting specific values and arbitrary values from a Dictionary. All the items from a dictionary can be deleted at once by using clear() method. 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) # Deleting a Key # using pop() Dict.pop(5) print("\nPopping specific element: ") print(Dict) # Deleting a Key # using popitem() Dict.popitem() print("\nPops first element: ") print(Dict) # Deleting entire Dictionary Dict.clear() print("\nDeleting Entire Dictionary: ") print(Dict) |
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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'}
Popping specific element:
{'A': {1: 'Geeks', 3: 'Geeks'}, 'B': {1: 'Geeks', 2: 'Life'}, 7: 'Geeks'}
Pops first element:
{'B': {1: 'Geeks', 2: 'Life'}, 7: 'Geeks'}
Deleting Entire Dictionary:
{}
Dictionary Methods
| Methods | Description |
|---|---|
| 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. |