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Python by Example: JSON Files

Reading and writing JSON files is common—config files, caches, API responses. Use json.load() to read from a file object and json.dump() to write. Both handle encoding. Use a context manager (with) so the file is closed properly.

What you'll learn:

  • json.dump() — write Python object to file
  • json.load() — read file into Python object
import json
import tempfile
import os

# Write to a file
data = {"name": "Alice", "scores": [85, 90, 78]}
with tempfile.NamedTemporaryFile(mode="w", suffix=".json", delete=False) as f:
    json.dump(data, f, indent=2)
    path = f.name

# Read from file
with open(path) as f:
    loaded = json.load(f)
print(loaded)
os.unlink(path)

dump and load work with file objects; dumps and loads work with strings. Use indent when writing for readability.

To run this program:

$ python source/json-files.py
{'name': 'Alice', 'scores': [85, 90, 78]}

Tip: For large files, consider ijson or streaming. For config, json.load() is usually sufficient.

Try it: Write a dict to a file, close it, then read it back and verify the data.

Source: json-files.py

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