demjson3

Warnings

• breaking Users migrating from the original `demjson` library to `demjson3` (especially in Python 3 environments) should update their `import` statements. `demjson3` is a dedicated Python 3 fork, resolving compatibility issues (`use_2to3` errors with newer `setuptools`) that plagued `demjson` in Python 3.
  Fix: For Python 3 projects, replace `demjson` with `demjson3` in `requirements.txt` and use `import demjson3`. If legacy code expects the `demjson` name, use `import demjson3 as demjson`.
• gotcha `demjson3` defaults to strict RFC 7159 compliance. This means non-standard JavaScript syntax (e.g., comments, unquoted keys, single-quoted strings, hexadecimal numbers, `undefined` keyword) will raise errors during decoding.
  Fix: If parsing JavaScript-like input that is not strictly JSON, set `strict=False` in the `decode()` method (e.g., `demjson3.decode(json_string, strict=False)`).
• gotcha When implementing `json_equivalent()` on custom Python classes for encoding, this method must return standard Python objects (dictionaries, lists, primitives) that `demjson3` can then encode. It should *not* return an already JSON-formatted string, as this will lead to double-encoding or incorrect output.
  Fix: Ensure `json_equivalent()` returns Python data structures, not `str`.
• gotcha `demjson3` automatically converts numbers that would lose precision as standard Python `float` types into `decimal.Decimal` objects during decoding to preserve accuracy.
  Fix: Be aware that numerical data might be returned as `Decimal` objects. Adjust downstream processing to handle `decimal.Decimal` types, or explicitly convert them to `float` if precision loss is acceptable.

Install

• pip install demjson3 Install latest version

Imports

• encode
  wrong:

  import demjson
  json_string = demjson.encode(python_object)

  correct:

  import demjson3
  json_string = demjson3.encode(python_object)

  demjson3 is the Python 3 native fork; direct `demjson` imports might be problematic or require older `setuptools` versions.
• decode
  wrong:

  import demjson
  python_object = demjson.decode(json_string)

  correct:

  import demjson3
  python_object = demjson3.decode(json_string)

  Use `demjson3` for Python 3 environments.

Quickstart

This quickstart demonstrates basic encoding and decoding of JSON data using `demjson3`. It shows how to convert Python dictionaries and lists to JSON strings and vice-versa. It also includes an example of using the `strict=False` option to parse more lenient, JavaScript-like JSON with features not allowed by RFC 7159.

import demjson3

# Encode Python data to JSON string
python_data = {'name': 'Alice', 'age': 30, 'isStudent': False, 'courses': ['Math', 'Science'], 'extra': None}
json_output = demjson3.encode(python_data, indent=2, strict=True)
print('Encoded JSON:')
print(json_output)

# Decode JSON string to Python data
json_input = '{"product": "Laptop", "price": 1200.50, "inStock": true}'
python_decoded = demjson3.decode(json_input)
print('\nDecoded Python data:')
print(python_decoded)

# Example of non-strict decoding (allowing comments and unquoted keys)
non_strict_json = "{ /* A comment */ myKey: 'value', another: undefined }"
python_non_strict = demjson3.decode(non_strict_json, strict=False)
print('\nDecoded non-strict JSON:')
print(python_non_strict)