# How to use Python dictionary The Python dictionary is an important data type in Python’s [internet programming language](https://www.ionos.com/digitalguide/websites/web-development/web-programming-languages/). It is used to link terms and meanings together. Key-value pairs are used to **create tables, data collections, or inventories**. The Python dictionary can also be used with [Python “for” loops](https://www.ionos.com/digitalguide/websites/web-development/python-for-loop/), [Python “if else” statements](https://www.ionos.com/digitalguide/websites/web-development/python-if-else/), and [Python “while” loops](https://www.ionos.com/digitalguide/websites/web-development/python-while-loop/). ## What is a Python dictionary? A Python dictionary is a data type which links terms and meanings. This structure allows **keys and values** to be linked, stored, and later retrieved. Similar to a regular dictionary where a term is associated with an explanation or translation, the Python dictionary creates an association table which cannot contain duplicates. This means that each key can only occur once. ## The structure of a Python dictionary A Python dictionary is always in curly braces. The key and its corresponding value are connected by a colon, and the resulting pairs are separated by commas. Theoretically, a Python dictionary may contain any number of key-value pairs. The key is enclosed in quotation marks. You probably already know how to write it from our [Python tutorial](https://www.ionos.com/digitalguide/websites/web-development/python-tutorial/ "Python tutorial"). See the example below: ```none ages = {'Jim': 42, 'Jack': 13, 'John': 69} ``` The Python dictionary is read by placing the correct key in square braces. Below you will find how it is written in code: ```none age_jim = ages['Jim'] assert age_jim == 42 ``` ## Python dictionary example The Python dictionary’s structure and functionality can be explained with a simple example. Countries and capitals are assigned and outputted in the following structure. The Python dictionary should look like this: ```none capitals = { "UK": "London", "FR": "Paris", "DE": "Berlin" } ``` Use the square braces to query a specific element: ```none capitals["FR"] assert capitals["FR"] == 'Paris' ``` The output would be the value associated with the key “France”, which would be “Paris”. ### Alternative structure You can also build a Python dictionary without content and fill it afterwards. An empty Python dictionary is always created first for this and it should look like this: ```none capitals = { } ``` Complete the Dictionary: ```none capitals["UK"] = "London" capitals["FR"] = "Paris" capitals["DE"] = "Berlin" ``` When you query the Python dictionary “capitals”, the following will be outputted: ```none { "UK": "London", "FR": "Paris", "DE": "Berlin" } ``` ## How do I change the Python dictionary? You can also modify your Python dictionary later on. Simply write the following to attach key-value pairs: ```none capitals[ "IT" ] = "Roma" print(capitals) ``` It should now look like this: ```none { "UK": "London", "FR": "Paris", "DE": "Berlin", "IT": "Roma" } ``` Use the following code to change a value within a key-value pair: ```none capitals = { "UK": "London", "FR": "Paris", "DE": "Berlin", "IT": "???" } assert capitals["IT"] == "???" capitals["IT"] = "Roma" assert capitals["IT"] == "Roma" ``` The output then reads: ```none { "UK": "London", "FR": "Paris", "DE": "Berlin", "IT": "Roma" } ``` ## How do I remove key-value pairs from the Python dictionary? There are three options available to subsequently remove a key-value pair from the Python dictionary: del, pop, and popitem. ### Remove with del A simple inventory is a good example of the del method. Let’s assume that a bakery offers 100 rolls, 25 loaves of bread, and 20 croissants when it opens for business. The corresponding Python dictionary would look like this: ```none stock = { "rolls": 100, "breads": 25, "croissants": 20 } ``` If the bakery has sold all its croissants and wants to delete them from its listing, the del command can be used to do this: ```none del stock["croissants"] print(stock) ``` You must make sure that you always use the del command in conjunction with a key-value pair with this method. Otherwise, the entire Python dictionary will be deleted. This is a [Python problem](https://www.ionos.com/digitalguide/websites/web-development/troubleshooting-common-python-problems/) which occurs relatively often. ### Remove with pop The second way to remove key-value pairs from a Python dictionary is pop. This stores the removed value in a new variable. It works as follows: ```none marbles = { "red": 13, "green": 19, "blue": 7, "yellow": 21} red_marbles = marbles.pop("red") print(f"We've removed {red_marbles} red marbles.") print(f"Remaining marbles are: {marbles}") ``` The output will look like this: ```none We've removed 13 red marbles. Remaining marbles are: {'green': 19, 'blue': 7, 'yellow': 21} ``` ### Remove with popitem Use popitem to remove the last key-value pair from your Python dictionary. This is the code: ```none last = marbles.popitem() print(last) print(marbles) ``` Your output will look like this: ```none ('yellow', 21) { "One": 1, "Two": 2, "Three": 3 } ``` ## Other methods for the Python dictionary There are a few other methods that work with a Python dictionary. Below is a list of the most important options:
Method Description
Clear Clear removes all key-value pairs from the Python dictionary.
Copy Copy creates a copy of the dictionary in storage.
Get Get determines the value by entering the key.
Keys Keys reads the keys of your dictionary.
Update Update extends a Python dictionary by one. Duplicate keys are overwritten in the attached dictionary.
Values Values queries all your dictionary’s values.
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