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

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Creating dictionaries

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

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creator = {'name' : 'Guido van Rossum', 'language' : 'Python'}\n\nprint(type(creator))\n# <class 'dict'>
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To create an empty dictionary, simply use a pair of curly brackets.

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

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tech = dict(mobile = 'React Native', web = 'React')\n\nprint(type(tech))\n# <class 'dict'>
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Get an item by its key or using get()

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

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lang_types = {'statically_typed' : 'Java', 'dynamically_typed' : 'Python'}\n\nprint(lang_types['statically_typed'])\n# Java
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We can also get the value of an item using the get() function which receives the item key as the argument.

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lang_types = {'statically_typed' : 'Java', 'dynamically_typed' : 'Python'}\n\nprint(lang_types.get('dynamically_typed'))\n# Python
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Get all the keys

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

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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.

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billionaires = {'Jeff Bezos' : 'Amazon', 'Elon Musk' : 'Tesla'}\n\nprint(billionaires.keys())\n# dict_keys(['Jeff Bezos', 'Elon Musk'])\n\nbillionaires_list = list(billionaires.keys())\n\nprint(billionaires_list)\n# ['Jeff Bezos', 'Elon Musk']\n\nprint(type(billionaires_list))\n# <class 'list'>
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Add or change an item by key

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

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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.

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ride = {'Uber' : 'America', 'Didi' : 'China'}\n\nride['Ola'] = 'India'\n\nprint(ride)\n# {'Uber': 'America', 'Didi': 'China', 'Ola': 'India'}
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We can assign a new value to a key using the = operator.

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ride = {'Uber' : 'America', 'Didi' : 'China'}\n\nride['Didi'] = 'Republic of China'\n\nprint(ride)\n# {'Uber': 'America', 'Didi': 'Republic of China'}
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Get all values

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

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

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parent = {'Audi' : 'Volkswagen', 'Alfa Romeo' : 'Stellantis', 'Jaguar' : 'Tata Motors'}\n\n\nprint(parent.values())\n# dict_values(['Volkswagen', 'Stellantis', 'Tata Motors'])\n\nprint(type(parent.values()))\n# <class 'dict_values'>\n\nprint(list(parent.values()))\n# ['Volkswagen', 'Stellantis', 'Tata Motors']\n\nprint(type(list(parent.values())))\n# <class 'list'>
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Get key : value pairs

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

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backend = {'Node' : 'JavaScript', 'Express' : 'Python'}\n\nprint(backend.items())\n# dict_items([('Node', 'JavaScript'), ('Express', 'Python')])
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Length of a dictionary

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

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me = {'first_name' : 'Hemanta', 'last_name' : 'Sundaray'}\n\nprint(len(me))\n# 2
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Combine dictionaries

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We can combine dictionaries using the update() function.

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person = {'first_name' : 'Hemanta', 'last_name' : 'Sundaray'}\n\nprofession = {'profession' : 'Retail Strategy'}\n\nperson.update(profession)\n\nprint(person)\n# {'first_name': 'Hemanta', 'last_name': 'Sundaray', 'profession': 'Retail Strategy'}
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Delete a key : value pair

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

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category = {'Web Development' : 'JavaScript', 'Data Science' : 'Python'}\n\ndel category['Web Development']\n\nprint(category)\n# {'Data Science': 'Python'}
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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.

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category = {'Web Development' : 'JavaScript', 'Data Science' : 'Python'}\n\npopped = category.pop('Data Science')\n\nprint(popped)\n# Python\n\nprint(category)\n# {'Web Development': 'JavaScript'}
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Delete all key : value pairs

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

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captain = {'name' : 'Ma Long', 'country' : 'China'}\n\ncaptain.clear()\n\nprint(captain)\n# {}
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Existence of a key

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

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car_models = {'hyundai' : ['Creta', 'Tucson'], 'Honda' : ['City', 'Civic']}\n\nprint('hyundai' in car_models)\n# True
\n","frontmatter":{"title":"A Comprehensive Guide to Python Dictionaries","date":"2021-08-20"}}},"pageContext":{"slug":"/a-comprehensive-guide-to-python-dictionaries/","prev":{"fields":{"slug":"/numpy-arrays-indexing-and-slicing/"},"frontmatter":{"modules":null}},"next":{"fields":{"slug":"/default-parameter-values-in-python-functions/"},"frontmatter":{"modules":null}}}}, "staticQueryHashes": ["3159585216"]}