Python Dictionary: Creating a Dictionary

A dictionary in Python stores data as key-value pairs. This page shows the main ways to create a dictionary, the basic syntax, and a few common beginner mistakes to avoid.

If you are new to dictionaries, you may also want to read Python dictionaries explained or what is a dictionary in Python.

Quick example

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

print(student)

Output:

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

Use curly braces with key-value pairs separated by commas. Keys and values are joined with a colon.

What this page covers

What a dictionary is
The basic syntax for creating one
Common ways to make a dictionary
Beginner mistakes to avoid

What a dictionary is

A dictionary stores data as key-value pairs.

A key is the label
A value is the data connected to that label

For example, in this dictionary:

student = {
    "name": "Ana"
}

"name" is the key
"Ana" is the value

Dictionaries are useful when your data has labels, such as:

name
age
email
country

Create a dictionary with curly braces

This is the most common way to create a dictionary.

Use {} and write each item as key: value.

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

print(student)

Output:

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

Syntax rules

Use {} to start and end the dictionary
Write each item as key: value
Separate items with commas
String keys are usually written in quotes

Example:

book = {
    "title": "Python Basics",
    "pages": 150,
    "available": True
}

print(book)

This style is best when you already know the keys and values you want to add.

Create an empty dictionary

Sometimes you want to start with an empty dictionary and add items later.

You can create an empty dictionary in two ways:

data = {}
print(data)

data = dict()
print(data)

Output:

{}

Both are correct.

Important beginner note

{} creates an empty dictionary, not an empty set.

If you want an empty set, you must use set().

my_dict = {}
my_set = set()

print(type(my_dict))
print(type(my_set))

Output:

<class 'dict'>
<class 'set'>

Create a dictionary with `dict()`

You can also use dict() to create a dictionary.

One simple way is with keyword arguments:

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

Output:

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

This can be easy to read for small dictionaries.

Important rule for `dict()`

When using keyword arguments:

keys must be valid Python names
you do not put quotes around the keys

This works:

user = dict(name="Sam", age=25)
print(user)

This does not work as keyword syntax:

# dict(first-name="Sam")

That key is not a valid Python name because it contains a hyphen.

If your keys are not valid Python names, use curly braces instead:

user = {
    "first-name": "Sam"
}

print(user)

Create a dictionary from pairs

dict() can also build a dictionary from key-value pairs.

This is useful when your data already exists as pairs, such as a list of tuples.

pairs = [("name", "Ana"), ("age", 20), ("city", "Lima")]

student = dict(pairs)

print(student)

Output:

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

You can also use tuples directly:

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

This approach is helpful when you receive data in pair form and want to turn it into a dictionary.

Rules beginners should know

Here are a few important dictionary rules:

Keys must be unique
If the same key appears more than once, the last value replaces earlier ones
Values can repeat
Keys are often strings, but other immutable types can also be keys

Duplicate key example

data = {
    "name": "Ana",
    "name": "Maria"
}

print(data)

Output:

{'name': 'Maria'}

Only the last value is kept.

Keys can be numbers too

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

print(scores)

Mutable types cannot be keys

A list cannot be a dictionary key because lists are mutable.

This will cause an error:

# bad = {
#     [1, 2]: "numbers"
# }

But a tuple can be used as a key because tuples are immutable:

good = {
    (1, 2): "numbers"
}

print(good)

When to use a dictionary

Use a dictionary when each value has a label.

Dictionaries are a good choice for:

user data
settings
counters
lookups

Example:

user = {
    "username": "ana123",
    "email": "ana@example.com",
    "logged_in": True
}

print(user["email"])

If you want to learn how to read values from a dictionary, see how to access values in a dictionary in Python.

A list is usually a better choice when:

labels are not needed
you mostly care about position
order matters more than named fields

Common mistakes

Beginners often make these mistakes when creating dictionaries:

Using commas instead of colons between keys and values
Forgetting quotes around string keys when needed
Repeating the same key and expecting both values to stay
Using a mutable type like a list as a dictionary key
Mixing up {} for dictionaries and sets

Mistake: using a comma instead of a colon

Wrong:

# student = {"name", "Ana"}

Correct:

student = {"name": "Ana"}
print(student)

Mistake: forgetting quotes around a string key

Wrong:

# student = {name: "Ana"}

This only works if name is already a variable. If you want the key to be the text "name", use quotes.

Correct:

student = {"name": "Ana"}
print(student)

Mistake: expecting duplicate keys to stay

data = {"age": 20, "age": 30}
print(data)

Output:

{'age': 30}

Helpful checks while learning

These quick commands can help you inspect a dictionary:

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

print(my_dict)
print(type(my_dict))
print(my_dict.keys())
print(my_dict.values())
print(len(my_dict))

Example output:

{'name': 'Ana', 'age': 20}
<class 'dict'>
dict_keys(['name', 'age'])
dict_values(['Ana', 20])
2

If you want to learn these methods in more detail, see Python dictionary keys(), Python dictionary values(), and Python dictionary items().

FAQ

How do I create an empty dictionary in Python?

Use {} or dict(). Both create an empty dictionary.

What is the easiest way to create a dictionary?

The easiest way is usually curly braces with key-value pairs, like {"name": "Ana", "age": 20}.

Can dictionary keys be numbers?

Yes. Keys can be numbers, strings, tuples, and other immutable types.

Can a dictionary have duplicate keys?

A dictionary can be written with duplicate keys, but only the last value for that key is kept.

What is the difference between `{}` and `dict()`?

{} is the most common literal syntax. dict() is a constructor and is useful for empty dictionaries, keyword arguments, or key-value pair data.