{"id":87,"date":"2024-01-25T10:00:39","date_gmt":"2024-01-25T10:00:39","guid":{"rendered":"https:\/\/learnpython.elegantwallp.com\/?p=87"},"modified":"2024-01-25T10:00:40","modified_gmt":"2024-01-25T10:00:40","slug":"python-dictionary","status":"publish","type":"post","link":"https:\/\/learnpython.elegantwallp.com\/2024\/01\/25\/python-dictionary\/","title":{"rendered":"Python Dictionary"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you\u2019ll learn about Python Dictionary which allows you to organize related information.<\/p>\n\n\n\n

Introduction to the Python Dictionary type<\/h2>\n\n\n\n

A Python dictionary is a collection of key-value pairs where each key is associated with a value.<\/p>\n\n\n\n

A value in the key-value pair can be a\u00a0number, a\u00a0string, a\u00a0list, a\u00a0tuple, or even another dictionary. In fact, you can use a value of any valid type in Python as the value in the key-value pair.<\/p>\n\n\n\n

A key in the key-value pair must be immutable. In other words, the key cannot be changed, for example, a number, a string, a tuple, etc.<\/p>\n\n\n\n

Python uses curly braces {}<\/code> to define a dictionary. Inside the curly braces, you can place zero, one, or many key-value pairs.<\/p>\n\n\n\n

The following example defines an empty dictionary:<\/p>\n\n\n\n

empty_dict = {}<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Typically, you define an empty dictionary before a loop, either\u00a0for loop\u00a0or\u00a0while loop. And inside the loop, you add key-value pairs to the dictionary.<\/p>\n\n\n\n
To find the type of a dictionary, you use the\u00a0type()<\/code>\u00a0function as follows:<\/p>\n\n\n\n
empty_dict = {} print(type(empty_dict)) <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
<class 'dict'><\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
The following example defines a dictionary with some key-value pairs:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
The person<\/code> dictionary has five key-value pairs that represent the first name, last name, age, favorite colors, and active status.<\/p>\n\n\n\n
Accessing values in a Dictionary<\/h2>\n\n\n\n
To access a value by key from a dictionary, you can use the square bracket notation or the get()<\/code> method.<\/p>\n\n\n\n
1) Using square bracket notation<\/h3>\n\n\n\n
To access a value associated with a key, you place the key inside square brackets:<\/p>\n\n\n\n
dict[key]<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
The following shows how to get the values associated with the key\u00a0first_name<\/code>\u00a0and\u00a0last_name<\/code>\u00a0in the\u00a0person<\/code>\u00a0dictionary:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } print(person['first_name']) print(person['last_name'])<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
John Doe<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
2) Using the get() method<\/h3>\n\n\n\n
If you attempt to access a key that doesn\u2019t exist, you\u2019ll get an error. For example:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } ssn = person['ssn']<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Error:<\/p>\n\n\n\n
Traceback (most recent call last): File \"dictionary.py\", line 15, in <module> ssn = person['ssn'] KeyError: 'ssn'<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
To avoid this error, you can use the\u00a0get()<\/code>\u00a0method of the dictionary:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } ssn = person.get('ssn') print(ssn) <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
None<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
If the key doesn\u2019t exist, the get()<\/code> method returns None<\/code> instead of throwing a KeyError<\/code>. Note that None<\/code> means no value exists.<\/p>\n\n\n\n
The get()<\/code> method also returns a default value when the key doesn\u2019t exist by passing the default value to its second argument.<\/p>\n\n\n\n
The following example returns the\u00a0'000-00-0000'<\/code>\u00a0string if the\u00a0ssn<\/code>\u00a0key doesn\u2019t exist in the\u00a0person<\/code>\u00a0dictionary:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } ssn = person.get('ssn', '000-00-0000') print(ssn)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
000-00-0000<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Adding new key-value pairs<\/h2>\n\n\n\n
Since a dictionary has a dynamic structure, you can add new key-value pairs to it at any time.<\/p>\n\n\n\n
To add a new key-value pair to a dictionary, you specify the name of the dictionary followed by the new key in square brackets along with the new value.<\/p>\n\n\n\n
The following example adds a new key-value pair to the\u00a0person<\/code>\u00a0dictionary:<\/p>\n\n\n\n
person['gender'] = 'Famale' <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Modifying values in a key-value pair<\/h2>\n\n\n\n
To modify a value associated with a key, you specify the dictionary name with the key in square brackets and the new value associated with the key:<\/p>\n\n\n\n
dict[key] = new_value<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
The following example modifies the value associated with the\u00a0age<\/code>\u00a0of the\u00a0person<\/code>\u00a0dictionary:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } person['age'] = 26 print(person)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
{'first_name': 'John', 'last_name': 'Doe', 'age': 26, 'favorite_colors': ['blue', 'green'], 'active': True}<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Removing key-value pairs<\/h2>\n\n\n\n
To remove a key-value pair by a key, you use the\u00a0del<\/code>\u00a0statement:<\/p>\n\n\n\n
del dict[key]<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
In this syntax, you specify the dictionary name and the key that you want to remove.<\/p>\n\n\n\n
The following example removes the key\u00a0'active'<\/code>\u00a0from the\u00a0person<\/code>\u00a0dictionary:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } del person['active'] print(person)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
{'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green']}<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Looping through a dictionary<\/h2>\n\n\n\n
To examine a dictionary, you can use a for<\/code> loop to iterate over its key-value pairs, or keys, or values.<\/p>\n\n\n\n
Note that since Python 3.7, when you loop through a dictionary, you\u2019ll get the key-value pairs in the same order that you insert them.<\/p>\n\n\n\n
1) Looping all key-value pairs in a dictionary<\/h3>\n\n\n\n
Python dictionary provides a method called items()<\/code> that returns an object which contains a list of key-value pairs as tuples in a list.<\/p>\n\n\n\n
For example:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } print(person.items())<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
dict_items([('first_name', 'John'), ('last_name', 'Doe'), ('age', 25), ('favorite_colors', ['blue', 'green']), ('active', True)])<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
To iterate over all key-value pairs in a dictionary, you use a\u00a0for<\/code>\u00a0loop with two variable\u00a0key<\/code>\u00a0and\u00a0value<\/code>\u00a0to\u00a0unpack each tuple\u00a0of the list:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } for key, value in person.items(): print(f\"{key}: {value}\")<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
first_name: John last_name: Doe age: 25 favorite_colors: ['blue', 'green'] active: True<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Note that you can use any variable name in the for<\/code> loop. They don\u2019t have to be the key<\/code> and value<\/code>.<\/p>\n\n\n\n
2) Looping through all the keys in a dictionary<\/h3>\n\n\n\n
Sometimes, you just want to loop through all keys in a dictionary. In this case, you can use a for<\/code> loop with the keys()<\/code> method.<\/p>\n\n\n\n
The keys()<\/code> method returns an object that contains a list of keys in the dictionary.<\/p>\n\n\n\n
For example:<\/p>\n\n\n\n
 person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } for key in person.keys(): print(key)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
first_name last_name age favorite_colors active<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
In fact, looping through all keys is the default behavior when looping through a dictionary. Therefore, you don\u2019t need to use the keys()<\/code> method.<\/p>\n\n\n\n
The following code returns the same output as the one in the above example:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } for key in person: print(key)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
3) Looping through all the values in a dictionary<\/h3>\n\n\n\n
The values()<\/code> method returns a list of values without any keys.<\/p>\n\n\n\n
To loop through all the values in a dictionary, you use a for loop with the\u00a0values()<\/code>\u00a0method:<\/p>\n\n\n\n
person = { 'first_name': 'John', 'last_name': 'Doe', 'age': 25, 'favorite_colors': ['blue', 'green'], 'active': True } for value in person.values(): print(value) <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
John Doe 25 ['blue', 'green'] True<\/code><\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
Summary: in this tutorial, you\u2019ll learn about Python Dictionary which allows you to organize related information. Introduction to the Python Dictionary type A Python dictionary is a collection of key-value pairs where each key is associated with a value. A value in the key-value pair can be a\u00a0number, a\u00a0string, a\u00a0list, a\u00a0tuple, or even another dictionary. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[20],"tags":[],"class_list":["post-87","post","type-post","status-publish","format-standard","hentry","category-6-dictionaries"],"_links":{"self":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/87","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/comments?post=87"}],"version-history":[{"count":1,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/87\/revisions"}],"predecessor-version":[{"id":88,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/87\/revisions\/88"}],"wp:attachment":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/media?parent=87"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/categories?post=87"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/tags?post=87"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}