Python Dictionaries Explained

A Python dictionary stores data as key-value pairs. It is one of the most useful built-in data types in Python.

Dictionaries are great when your data has labels such as name, age, or price. Instead of finding a value by position, you look it up by its key.

For example:

student = {"name": "Ana", "age": 20}

In this dictionary:

"name" is a key, and "Ana" is its value
"age" is a key, and 20 is its value

If you are completely new to the term, see what a dictionary in Python is.

Quick example

Use this example to see the most common dictionary tasks: create, read, update, add, and loop.

student = {"name": "Ana", "age": 20}

print(student["name"])
student["age"] = 21
student["city"] = "Madrid"

for key, value in student.items():
    print(key, value)

Expected output:

Ana
name Ana
age 21
city Madrid

What a dictionary is

A dictionary:

Stores data as key-value pairs
Uses each key to look up a value
Works well for labeled data
Is written with curly braces {}

Example:

person = {"name": "Ana", "age": 20}

This is different from a list. A list uses positions like 0, 1, and 2. A dictionary uses keys like "name" and "age".

When to use a dictionary

Use a dictionary when values need names instead of positions.

Common examples:

A student record
App settings
Word counters
Product details
Grouped data

Example:

settings = {
    "theme": "dark",
    "language": "English",
    "notifications": True
}

A dictionary is often a better choice than a list when you want fast lookup by key.

How to create a dictionary

You can create a dictionary with curly braces {}.

student = {"name": "Ana", "age": 20}
print(student)

Output:

{'name': 'Ana', 'age': 20}

Empty dictionary

data = {}
print(data)

Output:

{}

Using `dict()`

You can also create a dictionary with dict():

student = dict(name="Ana", age=20)
print(student)

Output:

{'name': 'Ana', 'age': 20}

If you want more ways to create one, see creating a dictionary in Python.

How to access dictionary values

Use square brackets with a key:

student = {"name": "Ana", "age": 20}

print(student["name"])

Output:

Ana

Using `get()`

If a key might not exist, use get().

student = {"name": "Ana", "age": 20}

print(student.get("name"))
print(student.get("city"))

Output:

Ana
None

This is safer than using square brackets when the key may be missing.

student = {"name": "Ana"}

# print(student["city"])   # This would raise an error
print(student.get("city"))

To learn more, see the Python dictionary get() method or how to access values in a dictionary in Python.

How to add and change items

To add a new item, assign a value to a new key.

student = {"name": "Ana", "age": 20}
student["city"] = "Paris"

print(student)

Output:

{'name': 'Ana', 'age': 20, 'city': 'Paris'}

To change an existing item, assign a new value to an existing key.

student = {"name": "Ana", "age": 20}
student["age"] = 21

print(student)

Output:

{'name': 'Ana', 'age': 21}

You can also change multiple items with the update() method.

How to remove items

Use pop() to remove a key and get its value back.

student = {"name": "Ana", "age": 20, "city": "Paris"}

removed_value = student.pop("city")

print(removed_value)
print(student)

Output:

Paris
{'name': 'Ana', 'age': 20}

Use del to remove a key without returning its value.

student = {"name": "Ana", "age": 20}

del student["age"]
print(student)

Output:

{'name': 'Ana'}

Use clear() to remove everything.

student = {"name": "Ana", "age": 20}

student.clear()
print(student)

Output:

{}

Be careful: removing a missing key can raise an error.

student = {"name": "Ana"}

# del student["age"]   # This would raise an error

For step-by-step help, see how to remove a key from a dictionary in Python.

Looping through a dictionary

You can loop through keys, values, or both.

Loop through keys

student = {"name": "Ana", "age": 20, "city": "Madrid"}

for key in student:
    print(key)

Loop through values

student = {"name": "Ana", "age": 20, "city": "Madrid"}

for value in student.values():
    print(value)

Loop through key-value pairs

This is often the easiest option when you need both the key and the value.

student = {"name": "Ana", "age": 20, "city": "Madrid"}

for key, value in student.items():
    print(key, value)

Possible output:

name Ana
age 20
city Madrid

You can learn more about items(), keys(), and values(), or see how to loop through a dictionary in Python.

Important dictionary rules

Here are some important rules beginners should know:

Keys must be unique
Keys should be immutable
Values can be any type
Dictionaries are mutable

Keys must be unique

If the same key appears more than once, the later value replaces the earlier one.

data = {"name": "Ana", "name": "Luis"}
print(data)

Output:

{'name': 'Luis'}

Keys should be immutable

Good key types include:

Strings
Numbers
Tuples

These work well because they do not change.

Values can be any type

A dictionary value can be a string, number, list, or even another dictionary.

student = {
    "name": "Ana",
    "age": 20,
    "grades": [90, 85, 88],
    "address": {"city": "Madrid", "zip": "28001"}
}

print(student)

Dictionaries are mutable

This means you can change them after creation.

student = {"name": "Ana"}
student["name"] = "Eva"

print(student)

Dictionary methods to learn next

These methods are very useful:

get() for safe lookup
keys() to view all keys
values() to view all values
items() to work with key-value pairs
update() to merge or change multiple items

Example:

student = {"name": "Ana", "age": 20}

print(student.keys())
print(student.values())
print(student.items())

student.update({"age": 21, "city": "Madrid"})
print(student)

Output:

dict_keys(['name', 'age'])
dict_values(['name', 20])
dict_items([('name', 'Ana'), ('age', 20)])
{'name': 'Ana', 'age': 21, 'city': 'Madrid'}

Common beginner problems

Here are some common mistakes when working with dictionaries.

Using a key that does not exist

This causes a KeyError if you use square brackets.

student = {"name": "Ana"}

# print(student["age"])   # KeyError
print(student.get("age"))  # Safer

If you are seeing this error, read KeyError in Python: causes and fixes.

Confusing dictionaries with lists

A dictionary does not use list positions like 0 and 1.

student = {"name": "Ana", "age": 20}

# print(student[0])   # Wrong
print(student["name"])  # Correct

Trying to use duplicate keys

Only the last value is kept.

data = {"color": "red", "color": "blue"}
print(data)

Output:

{'color': 'blue'}

Forgetting that keys are case-sensitive

These are different keys:

data = {"Name": "Ana", "name": "Luis"}
print(data)

Output:

{'Name': 'Ana', 'name': 'Luis'}

Using brackets instead of `get()` when a key may be missing

Use get() when you are not sure a key exists.

Useful debugging checks

If your dictionary code is not working, these quick checks can help:

print(my_dict)
print(my_dict.keys())
print(my_dict.values())
print(my_dict.items())
print(type(my_dict))
print('name' in my_dict)

These are useful for spotting:

Misspelled keys
Wrong data type
Missing keys
Unexpected dictionary contents

FAQ

What is a Python dictionary?

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

How is a dictionary different from a list?

A list uses positions called indexes. A dictionary uses keys like names or labels.

Can dictionary keys be duplicated?

No. If the same key appears more than once, the later value replaces the earlier one.

Can dictionary values have different data types?

Yes. One dictionary can store strings, numbers, lists, or other dictionaries as values.

How do I safely get a value from a dictionary?

Use get(), because it does not raise an error when the key is missing.