How to Convert Dictionary to JSON in Python

If you want to turn a Python dictionary into JSON, use the built-in json module.

• Use json.dumps() when you want a JSON string
• Use json.dump() when you want to write JSON to a file

This page shows both methods with simple examples.

Quick answer #

import json

data = {"name": "Alice", "age": 25, "active": True}
json_text = json.dumps(data)
print(json_text)

Output:

{"name": "Alice", "age": 25, "active": true}

Use json.dumps() when you want a JSON string. Use json.dump() when you want to save JSON directly to a file.

What this page helps you do #

• Convert a Python dictionary into a JSON string
• Save dictionary data as JSON in a file
• Understand the difference between json.dumps() and json.dump()
• Avoid common beginner mistakes when working with JSON

When to use dictionary to JSON conversion #

Convert a dictionary to JSON when:

• Sending data to an API
• Saving structured data to a file
• Sharing data between Python and other languages
• Creating text output in JSON format

If you are new to dictionaries, see what a Python dictionary is.

Convert a dictionary to a JSON string with json.dumps() #

json.dumps() takes a Python object and returns a string in JSON format.

Steps:

• Import the built-in json module
• Pass the dictionary to json.dumps()
• Store or print the returned string

import json

data = {
    "name": "Alice",
    "age": 25,
    "active": True
}

json_text = json.dumps(data)

print(json_text)
print(type(json_text))

Output:

{"name": "Alice", "age": 25, "active": true}
<class 'str'>

Important points:

• data is a Python dictionary
• json_text is a string
• Python True becomes JSON true

Use this when you want to:

• Print JSON
• Send JSON in a web request
• Return JSON from a function
• Store JSON in a variable

For a deeper explanation, see json.dumps() explained.

Write a dictionary to a JSON file with json.dump() #

json.dump() writes JSON directly into a file.

Steps:

• Open a file in write mode
• Pass the dictionary and file object to json.dump()
• The JSON text is written to the file

import json

data = {
    "name": "Alice",
    "age": 25,
    "active": True
}

with open("data.json", "w") as file:
    json.dump(data, file)

This creates a file named data.json.

The file content will look like this:

{"name": "Alice", "age": 25, "active": true}

Use this when you want to save JSON to disk instead of keeping it in a Python string.

For more detail, see json.dump() explained.

Make JSON easier to read #

JSON often looks better when it is formatted.

You can use:

• indent=4 to add spacing
• sort_keys=True to sort keys alphabetically

Pretty-print a JSON string #

import json

data = {
    "name": "Alice",
    "age": 25,
    "active": True
}

json_text = json.dumps(data, indent=4, sort_keys=True)
print(json_text)

Output:

{
    "active": true,
    "age": 25,
    "name": "Alice"
}

Write formatted JSON to a file #

import json

data = {
    "name": "Alice",
    "age": 25,
    "active": True
}

with open("data.json", "w") as file:
    json.dump(data, file, indent=4, sort_keys=True)

Pretty formatting is useful when:

• Reading saved files
• Checking your output
• Debugging data problems

You can also read how to pretty-print JSON in Python.

How Python values map to JSON values #

When you convert a dictionary to JSON, Python values are changed into JSON values.

Example:

import json

data = {
    "name": "Alice",
    "skills": ["Python", "JSON"],
    "active": True,
    "manager": None
}

print(json.dumps(data, indent=4))

Output:

{
    "name": "Alice",
    "skills": [
        "Python",
        "JSON"
    ],
    "active": true,
    "manager": null
}

JSON objects are expected to use string keys. In practice, your dictionary keys should be strings when exporting to JSON.

For a broader overview, see the Python json module overview.

Values that cannot be converted directly #

Some Python values are not supported by JSON by default.

Common examples:

• set
• Custom objects
• Functions

This code causes an error because a set is not JSON serializable:

import json

data = {
    "name": "Alice",
    "tags": {"python", "json"}
}

print(json.dumps(data))

You will get an error like:

TypeError: Object of type set is not JSON serializable

Fix unsupported values before converting #

Convert unsupported values into supported ones first.

For example, change a set into a list:

import json

data = {
    "name": "Alice",
    "tags": list({"python", "json"})
}

print(json.dumps(data, indent=4))

Output:

{
    "name": "Alice",
    "tags": [
        "python",
        "json"
    ]
}

A good rule is:

• Convert sets to lists
• Convert custom objects to dictionaries
• Convert special values to strings if needed

Beginner debugging checks #

If your conversion is not working, check these first:

• Make sure your variable is really a dictionary
• Look for unsupported data types like set
• Print the type before converting
• Read the full error message carefully

Useful debugging commands:

print(type(data))
print(data)

import json
print(json.dumps(data, indent=4))

Run your script from the terminal if needed:

python your_script.py

If you already have JSON text and want to turn it back into Python data, read how to parse JSON in Python.

Common mistakes #

These are common beginner mistakes when converting a dictionary to JSON:

• Using json.dump() when you wanted a string instead of a file write
• Using json.dumps() and expecting it to save to a file automatically
• Trying to convert unsupported types like set
• Forgetting to import the json module
• Opening the output file with the wrong mode

Example of a common mix-up:

import json

data = {"name": "Alice"}

# This returns a string, but does not save a file
json_text = json.dumps(data)

If you want to save to a file, use:

import json

data = {"name": "Alice"}

with open("data.json", "w") as file:
    json.dump(data, file)

FAQ #

What is the difference between json.dump() and json.dumps()? #

json.dump() writes JSON to a file. json.dumps() returns JSON as a string.

Can I convert a nested dictionary to JSON? #

Yes. Nested dictionaries and lists can be converted as long as the values are JSON serializable.

Why does Python say an object is not JSON serializable? #

It means the value is not a supported JSON type, such as a set or custom object.

How do I make JSON output readable? #

Use indent=4 in json.dumps() or json.dump() to pretty-print the result.

See also #

• Python json module overview
• json.dumps() function explained
• json.dump() function explained
• How to parse JSON in Python
• How to pretty-print JSON in Python
• What is a Python dictionary?