In Python, a dictionary is a set of key : value pairs.

• The keys in a dictionary must be unique.

• The keys can be any immutable data type.

• Dictionaries are mutable. This means that we can add, delete and change key : value pairs.

Creating dictionaries

We can create a dictionary by placing comma separated key : value pairs within curly brackets.

creator = {'name' : 'Guido van Rossum', 'language' : 'Python'}

print(type(creator))
# <class 'dict'>

To create an empty dictionary, simply use a pair of curly brackets.

We can also create a dictionary by passing named arguments and values to the dict() function.

tech = dict(mobile = 'React Native', web = 'React')

print(type(tech))
# <class 'dict'>

Get an item by its key or using get()

We can get the value of an item by its key.

lang_types = {'statically_typed' : 'Java', 'dynamically_typed' : 'Python'}

print(lang_types['statically_typed'])
# Java

We can also get the value of an item using the get() function which receives the item key as the argument.

lang_types = {'statically_typed' : 'Java', 'dynamically_typed' : 'Python'}

print(lang_types.get('dynamically_typed'))
# Python

Get all the keys

We can get all the keys of a dictionary using the keys() function.

The keys() function returns dict_keys(), which is an iterable view of the keys. We can convert the dict_keys() object to a list using the list() function.

billionaires = {'Jeff Bezos' : 'Amazon', 'Elon Musk' : 'Tesla'}

print(billionaires.keys())
# dict_keys(['Jeff Bezos', 'Elon Musk'])

billionaires_list = list(billionaires.keys())

print(billionaires_list)
# ['Jeff Bezos', 'Elon Musk']

print(type(billionaires_list))
# <class 'list'>

Add or change an item by key

We can add an item to a dictionary by referring to the item by its key and assigning a value.

If the key is already present in the dictionary, its existing value is replaced by the new value. If the key is not present, then the new key is added to the dictionary along with its associated value.

ride = {'Uber' : 'America', 'Didi' : 'China'}

ride['Ola'] = 'India'

print(ride)
# {'Uber': 'America', 'Didi': 'China', 'Ola': 'India'}

We can assign a new value to a key using the = operator.

ride = {'Uber' : 'America', 'Didi' : 'China'}

ride['Didi'] = 'Republic of China'

print(ride)
# {'Uber': 'America', 'Didi': 'Republic of China'}

Get all values

We can extract all the values of a dictionary using the values() function.

The values() function returns a dict_values object, which we can then convert to an object using the list() function.

parent = {'Audi' : 'Volkswagen', 'Alfa Romeo' : 'Stellantis', 'Jaguar' : 'Tata Motors'}


print(parent.values())
# dict_values(['Volkswagen', 'Stellantis', 'Tata Motors'])

print(type(parent.values()))
# <class 'dict_values'>

print(list(parent.values()))
# ['Volkswagen', 'Stellantis', 'Tata Motors']

print(type(list(parent.values())))
# <class 'list'>

Get key : value pairs

We can extract the key : value pairs from a dictionary using the items() function. Each key : value pair is returned as a tuple.

backend = {'Node' : 'JavaScript', 'Express' : 'Python'}

print(backend.items())
# dict_items([('Node', 'JavaScript'), ('Express', 'Python')])

Length of a dictionary

We can count the number of key : value pairs in a dictionary using the len() function.

me = {'first_name' : 'Hemanta', 'last_name' : 'Sundaray'}

print(len(me))
# 2

Combine dictionaries

We can combine dictionaries using the update() function.

person = {'first_name' : 'Hemanta', 'last_name' : 'Sundaray'}

profession = {'profession' : 'Retail Strategy'}

person.update(profession)

print(person)
# {'first_name': 'Hemanta', 'last_name': 'Sundaray', 'profession': 'Retail Strategy'}

Delete a key : value pair

We can delete a key : value pair using the del keyword.

category = {'Web Development' : 'JavaScript', 'Data Science' : 'Python'}

del category['Web Development']

print(category)
# {'Data Science': 'Python'}

We can delete a key : value pair using the pop() method as well. The pop() method takes in the key and returns the associated value. The key : value pair is deleted from the dictionary.

category = {'Web Development' : 'JavaScript', 'Data Science' : 'Python'}

popped = category.pop('Data Science')

print(popped)
# Python

print(category)
# {'Web Development': 'JavaScript'}

Delete all key : value pairs

We can delete all key : value pairs using the clear() function.

captain = {'name' : 'Ma Long', 'country' : 'China'}

captain.clear()

print(captain)
# {}

Existence of a key

We can check whether a key exists in a dictionary or not using the in operator.

car_models = {'hyundai' : ['Creta', 'Tucson'], 'Honda' : ['City', 'Civic']}

print('hyundai' in car_models)
# True