In this article, you will learn the basics of dictionaries in Python. You will learn how to create dictionaries,
access the elements inside them, and how to modify them depending on your needs. You will also learn some of the most common built-in methods used on dictionaries. Here is what we will cover: A dictionary in Python is made up of key-value pairs. In the two sections that follow you will see two ways of creating a dictionary. The first way is by using a set of curly braces,
To create an empty dictionary, first create a variable name which will be the name of the dictionary. Then, assign the variable to an empty set of curly braces, Another way of creating an empty dictionary is to use the It acts as a constructor and creates an empty dictionary: To create a dictionary with items, you need to include key-value pairs inside the curly braces. The general syntax for this is the following: Let's break it down: Let's see an example of creating a dictionary with items: In the example above, there is a sequence of elements within the curly braces. Specifically,
there are three key-value pairs: The keys are When there are multiple key-value pairs in a dictionary, each key-value pair is separated from the next with a comma, Let's see another example. Say that you want to create a dictionary with items using the You would achieve this by
using
It's worth mentioning the It takes a predefined sequence of items as an argument and returns a new dictionary with the items in the sequence set as the dictionary's specified keys. You can optionally set a value for all the keys, but by default the value for the keys will
be The general syntax for the method is the following:
Let's see an example of creating a dictionary using
Now let's see another example that sets a value that will be the same for all the keys in the dictionary:
An Overview of Keys and Values in Dictionaries in PythonKeys inside a Python dictionary can only be of a type that is immutable. Immutable data types in Python are Dictionary keys cannot be of a type that is mutable, such as So, say you have the following dictionary:
The keys in the dictionary are If you try to create a key which is of
a mutable type you'll get an error - specifically the error will be a
In the example above, I tried to create a key which was of When it comes to values inside a Python dictionary there are no restrictions. Values can be of any data type - that is they can be both of mutable and immutable types. Another thing to note about the differences between keys and values in Python dictionaries, is the fact that keys are unique. This means that a key can only appear once in the dictionary, whereas there can be duplicate values. How to Find the Number of key-value Pairs Contained in a Dictionary in PythonThe When a dictionary is passed as an argument to the function, it returns the total number of key-value pairs enclosed in the dictionary. This is how you calcualte the number of key-value pairs using
How to View All key-value Pairs Contained in a Dictionary in PythonTo view every key-value pair that is inside a dictionary, use the built-in
The How to View All keys Contained in a Dictionary in PythonTo see all of the keys that are inside a dictionary, use the built-in
The How to View All values Contained in a Dictionary in PythonTo see all of the values that are inside a dictionary, use the built-in
The How to Access Individual Items in A Dictionary in PythonWhen working with lists, you access list items by mentioning the list name and using square bracket notation. In the square brackets you specify the item's index number (or position). You can't do exactly the same with dictionaries. When working with dictionaries, you can't access an element by referencing its index number, since dictionaries contain key-value pairs. Instead, you access the item by using the dictionary name and square bracket notation, but this time in the square brackets you specify a key. Each key corresponds with a specific value, so you mention the key that is associated with the value you want to access. The general syntax to do so is the following:
Let's look at the following example on how to access an item in a Python dictionary:
What happens though when you try to access a key that doesn't exist in the dictionary?
It results in a One way to avoid this from happening is to first search to see if the key is in the dictionary in the first place. You do this by using the
Another way around this is to access items in the dictionary by using the You pass the key you're looking for as an argument and
As you notice, when you are searching for a key that does
not exist, by default If instead of showing that default You do so by passing the new value as the second optional argument to the
Now when you are searching for a key and it is not contained in the dictionary, you will see the message How to Modify A Dictionary in PythonDictionaries are mutable, which means they are changeable. They can grow and shrink throughout the life of the program. New items can be added, already existing items can be updated with new values, and items can be deleted. How to Add New Items to A Dictionary in PythonTo add a key-value pair to a dictionary, use square bracket notation. The general syntax to do so is the following:
First, specify the name of the dictionary. Then, in square brackets, create a key and assign it a value. Say you are starting out with an empty dictionary:
Here is how you would add a key-value pair to
Here is how you would add another new key-value pair:
Keep in mind that if the key you are trying to add already exists in that dictionary and you are assigning it a different value, the key will end up being updated. Remember that keys need to be unique.
If you want to prevent changing the value of an already existing key by accident, you might want to check if the key you are trying to add is already in the dictionary. You do this by using the
How to Update Items in A Dictionary in PythonUpdating items in a dictionary works in a similar way to adding items to a dictionary. When you know you want to update one existing key's value, use the following general syntax you saw in the previous section:
To update a dictionary, you can also use the built-in This method is particularly helpful when you want to update more than one value inside a dictionary at the same time. Say
you want to update the
The The keys that already existed were updated with the new values that were assigned, and a new key-value pair was added. The Say you have one dictionary, If you want to merge the
contents of All the key-value pairs contained in
How to Delete Items from A Dictionary in PythonOne of the ways to delete a specific key and its associated value from a dictionary is by using the The syntax to do so is the following:
For example, this is how you would delete the
If you want to remove a key, but would also like to save that removed value, use the built-in The You pass the key you want to remove as an argument to the method. Here is the general syntax to do that:
To remove the
If you specify a key that does not exist in the dictionary you will get a
A way around this is to pass a second argument to the By including the second argument there would be no error. Instead, there would be a silent fail if the key didn't exist, and the dictionary would remain unchanged.
The For that, use the built-in This is general syntax for the
The
Lastly, if you want to delete all
key-value pairs from a dictionary, use the built-in
Using this method will leave you with an empty dictionary. ConclusionAnd there you have it! You now know the basics of dictionaries in Python. I hope you found this article useful. To learn more about the Python programming language, check out freeCodeCamp's Scientific Computing with Python Certification. You'll start from the basics and learn in an interacitve and beginner-friendly way. You'll also build five projects at the end to put into practice and help reinforce what you've learned. Thanks for reading and happy coding! Learn to code for free. freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. Get started Which method would you use to return the value associated with a specific key and remove that keyThe pop method accepts a key as an argument, returns the value that is associated with that key, and removes that key-value pair from the dictionary.
Which dictionary method returns the value associated with a specified key if the key is not found it returns a default value?Python Dictionary get() Method Syntax:
key: The key name of the item you want to return the value from. Value: (Optional) Value to be returned if the key is not found. The default value is None.
What method is used to retrieve the value from a dictionary associated with a given key?The get() method returns the value for the specified key if the key is in the dictionary.
How do you remove a key from a dictionary?Because key-value pairs in dictionaries are objects, you can delete them using the “del” keyword. The “del” keyword is used to delete a key that does exist. It raises a KeyError if a key is not present in a dictionary.
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