What Is a Dictionary in Python?

A dictionary in Python is a way to store related data using keys and values.

This is useful when your data has labels. For example, a person can have a name, age, and city. Instead of storing those values by position, a dictionary stores them by name.

This page explains the basic idea of a dictionary, what it stores, and when to use one.

Quick example #

person = {
    "name": "Alice",
    "age": 25,
    "city": "Paris"
}

print(person["name"])
print(person["age"])

Output:

Alice
25

Use a dictionary when you want to store related values using names called keys.

Simple definition #

A dictionary is a Python data type that stores data as key-value pairs.

A key is the name you use to find a value
A value is the data stored for that key
Dictionaries are useful when data has labels like name, age, or price

You will often see dictionaries used for:

user information
settings
product details
lookup data

What key-value pairs look like #

Here is a simple dictionary:

person = {"name": "Alice"}

In this example:

"name" is the key
"Alice" is the value

A dictionary connects the key to the value.

Some important points:

Each key points to one value
Keys in the same dictionary should be unique
Keys are often strings, but they do not have to be

For example, number keys also work:

scores = {
    1: "low",
    2: "medium",
    3: "high"
}

print(scores[2])

Output:

medium

Why dictionaries are useful #

Dictionaries are useful because they make data easier to read and understand.

Instead of remembering that person[0] is a name and person[1] is an age, you can use clear labels like:

person["name"]
person["age"]

This makes dictionaries a good choice for:

storing records
saving settings
mapping one value to another
looking up data by name or ID

They are often easier to read than long lists when the data is labeled.

Basic dictionary example #

You create a dictionary with curly braces {}.

Separate each key-value pair with a comma
Use a colon : between each key and value
Access a value with square brackets and the key

Example:

book = {
    "title": "Python Basics",
    "pages": 200,
    "price": 19.99
}

print(book["title"])
print(book["price"])

Output:

Python Basics
19.99

In this example:

"title" is a key
"Python Basics" is its value
book["title"] gets the value for that key

If you want to learn the syntax in more detail, see creating a dictionary in Python.

Important beginner facts #

There are a few important things beginners should know about dictionaries.

Dictionaries are mutable, which means you can change them after creating them
You can add new key-value pairs later
You can update existing values
Dictionary keys are not based on numeric positions like list indexes

Example:

person = {"name": "Alice", "age": 25}

person["age"] = 26
person["city"] = "Paris"

print(person)

Output:

{'name': 'Alice', 'age': 26, 'city': 'Paris'}

This means dictionaries are flexible. You can start with a small set of data and change it as needed.

Dictionary vs list #

A dictionary is not the same as a list.

Use a list when:

order matters
positions matter
you want to access items by index like items[0]

Use a dictionary when:

labels matter
you want named values
you want to access data by keys like person["name"]

Example of a list:

colors = ["red", "green", "blue"]
print(colors[0])

Example of a dictionary:

person = {"name": "Alice", "age": 25}
print(person["name"])

Lists use indexes like numbers. Dictionaries use keys like names or IDs.

If you want a broader comparison, see when to use lists vs tuples vs sets vs dictionaries.

Common beginner confusion #

Here are some common mistakes beginners make with dictionaries.

A dictionary is not the same as a list
You do not get values with person[0] unless 0 is actually a key
Missing keys can cause a KeyError
Keys are often strings, but they do not have to be

Example of a mistake:

person = {"name": "Alice", "age": 25}

print(person[0])

This will cause an error because 0 is not a key in the dictionary.

Common mistakes #

Trying to access a dictionary value with a list-style index
Using a key that does not exist
Confusing keys with values
Assuming dictionaries are only for strings

Example of a missing key:

person = {"name": "Alice"}

print(person["age"])

This raises a KeyError because "age" is not in the dictionary.

A safer option is often the get() method:

person = {"name": "Alice"}

print(person.get("age"))

Output:

None

To learn more, see Python dictionary get() and KeyError in Python: causes and fixes.

Useful debugging checks #

If you are not sure what your dictionary contains, these simple checks help:

print(my_dict)
print(my_dict.keys())
print(type(my_dict))
print("name" in my_dict)

These can help you answer questions like:

Is this really a dictionary?
What keys does it have?
Does a specific key exist?

Next steps #

Once you understand the basic idea, the next step is using dictionaries in simple tasks.

Good next topics are:

FAQ #