Dictionary (Dict) 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 the key: value pair. Key-value is provided in the dictionary to make it more optimized.
Note – Keys in a dictionary don’t allow Polymorphism.
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 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.
# 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{}.
# 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:
# Creating a Nested Dictionary
# as shown in the below image
Dict = {1: 'Geeky', 2: 'For',
3:{'A' : 'Welcome', 'B' : 'To', 'C' : 'Codes'}}
print(Dict)
Output:
{1: 'Geeky', 2: 'For', 3: {'A': 'Welcome', 'B': 'To', 'C': 'Codes'}}
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.
# 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.
# Creating an empty Dictionary
Dict = {}
print("Empty Dictionary: ")
print(Dict)
# Adding elements one at a time
Dict[0] = 'Geeks'
Dict[2] = 'cds'
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' : 'Geeky'}}
print("\nAdding a Nested Key: ")
print(Dict)
Output:
Accessing a element using key: cds Accessing a element using key: Geeks
There is also a method called get() that will also help in accessing the element from a dictionary.
# Creating a Dictionary
Dict = {1: 'Geeky', 'name': 'geeky', 3: 'codes'}
# accessing a element using get()
# method
print("Accessing a element using get:")
print(Dict.get(3))
Output:
Accessing a element using get: codes
Accessing an element of a nested dictionary
In order to access the value of any key in the nested dictionary, use indexing [] syntax.
# Creating a Dictionary
Dict = {'Dict1': {1: 'Geeky'},
'Dict2': {'Name': 'Codes'}}
# Accessing element using key
print(Dict['Dict1'])
print(Dict['Dict1'][1])
print(Dict['Dict2']['Name'])
Output:
{1: 'Geeky'}
Geeky
Codes
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.
# 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'}
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. |
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