How to Write a Dict to a Pretty JSON File with Indent in Python

Serializes a Python dictionary to a readable JSON file using json.dump with indentation and sorted keys, then prints the file contents to stdout.

Easy Python 3.9+ Aug 9, 2026 Files & data 14 views 0 copies

json files serialization pretty-print

Python code

17 lines

Python 3.9+

import json
from pathlib import Path

data = {
    "name": "Python",
    "version": 3.12,
    "features": ["simple", "readable", "powerful"],
    "nested": {"creator": "Guido van Rossum", "year": 1991}
}

output_path = Path("output.json")

with output_path.open("w", encoding="utf-8") as f:
    json.dump(data, f, indent=4, sort_keys=True)

print(f"Written to {output_path}")
print(output_path.read_text(encoding="utf-8"))

Output

stdout

Written to output.json
{
    "name": "Python",
    "version": 3.12,
    "features": [
        "simple",
        "readable",
        "powerful"
    ],
    "nested": {
        "creator": "Guido van Rossum",
        "year": 1991
    }
}

How it works

The json.dump call writes the dictionary directly to the file object, with indent=4 adding four spaces per nesting level and sort_keys=True ordering keys alphabetically for stable, consistent output. Using Path.open in a with statement guarantees the file is closed properly even if an error occurs. The encoding is set to UTF-8, which is the default for JSON and safe for non-ASCII characters. The final read_text call verifies the written content by displaying it back to the console.

Common mistakes

Using `json.dumps` and forgetting to write the resulting string manually instead of `json.dump` for direct file writing.
Omitting `encoding='utf-8'` which can cause issues with non-ASCII characters on some platforms.
Forgetting to close the file if not using a `with` block, leaking file handles.
Confusing `indent` with `separators` — indent only affects whitespace, separators control delimiters.

Variations

Use `json.dump(data, f, indent=2)` for a more compact but still readable format.
Write to a string with `json.dumps(data, indent=4, sort_keys=True)` if you need to pass it elsewhere.

Real-world use cases

Exporting configuration or settings dicts from a web app to a human-readable config file on the server.
Persisting analysis results or model outputs from a data pipeline as readable JSON for easy inspection and sharing.
Creating fixture files for automated tests that need stable, nicely formatted JSON data to assert against.

How to Write a Dict to a Pretty JSON File with Indent in Python

Python code

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How it works

Common mistakes

Variations

Real-world use cases

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