Standard JSON

Common errors

• TypeError: Object of type datetime.date is not JSON serializable

  cause Attempting to serialize `datetime.date` (or `datetime.datetime`, `datetime.time`, `decimal.Decimal`) objects using the standard `json.dumps` function without specifying `StandardJSONEncoder`.
  fix Pass `cls=StandardJSONEncoder` to `json.dumps()` or `json.dump()`. Example: `json.dumps(data, cls=StandardJSONEncoder)`.

• AttributeError: module 'standardjson' has no attribute 'StandardJSONEncoder'

  cause This error occurs if `StandardJSONEncoder` is not exposed directly in the `standardjson` top-level package or if an older version (pre-0.3.0) is in use with an incorrect import path, or if `__init__.py` does not re-export it.
  fix Try importing explicitly from the `encoders` submodule: `from standardjson.encoders import StandardJSONEncoder`. Ensure you are on version 0.3.0 or later for this path.

• json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

  cause Attempting to decode a string that is not valid JSON, such as one with single quotes instead of double quotes for keys/strings, unquoted keys, or trailing commas.
  fix Ensure the JSON string strictly adheres to the JSON specification (e.g., all keys and string values must be double-quoted, no trailing commas, no comments). Use a JSON validator to identify syntax errors.

Warnings

• deprecated The `standardjson` library appears unmaintained, with its last release (0.3.1) in May 2014. It has not received updates for Python 3.6+ compatibility or recent JSON specification changes.
  Fix: Consider using more actively maintained alternatives like `orjson`, `jsons`, or handling custom types with the `default` parameter of the standard `json` library for modern Python applications.
• breaking Version 0.3.0 introduced breaking changes, including renaming the package to `standardjson` and moving `StandardJSONEncoder` into the `encoders` submodule.
  Fix: If upgrading from pre-0.3.0, update imports from `from standardjson import StandardJSONEncoder` to `from standardjson.encoders import StandardJSONEncoder` if the top-level import is not resolved.
• gotcha The library was primarily tested for Python 2.6, 2.7, and 3.3. While it might run on newer Python versions (3.4, 3.5), it is not officially supported or tested beyond these versions, which may lead to unexpected behavior or incompatibilities on Python 3.6+.
  Fix: Thoroughly test on your target Python version or use a more modern JSON serialization library that explicitly supports your Python runtime.
• gotcha Despite its name, Python's built-in `json` module is not strictly compliant with the JSON specification (ECMA-404 / RFC 8259) by default, particularly regarding `NaN`, `Infinity`, and `-Infinity` floating-point values which it encodes as their JavaScript equivalents rather than raising an error. `standardjson` aims for stricter compliance.
  Fix: Be aware of these differences, especially when interacting with systems expecting strict JSON compliance. `standardjson` itself aims to adhere to the spec, but ensure the final output is validated against your receiving system's expectations if using other tools in the pipeline.

Install

• pip install standardjson Install with pip

Imports

• StandardJSONEncoder

  from standardjson import StandardJSONEncoder

• StandardJSONEncoder (pre-0.3.0)
  wrong:

  from standardjson import StandardJSONEncoder

  correct:

  from standardjson.encoders import StandardJSONEncoder

  In versions 0.3.0 and later, StandardJSONEncoder was moved to the 'encoders' module, though the top-level import might be re-exposed via __init__.py in 0.3.1. For strictness, or if the top-level import fails, use the explicit path.

Quickstart

Use `StandardJSONEncoder` as you would use `json.JSONEncoder` from the Python standard library, passing it to the `cls` argument of `json.dumps()` or `json.dump()`.

import datetime
import json
from standardjson import StandardJSONEncoder

# Example with datetime.date
data = {'event_date': datetime.date(2023, 1, 15)}
json_output = json.dumps(data, cls=StandardJSONEncoder, indent=2)
print(f"Serialized date: {json_output}")
# Expected output: {"event_date": "2023-01-15"}

import decimal

# Example with decimal.Decimal
data_decimal = {'price': decimal.Decimal('19.99')}
json_output_decimal = json.dumps(data_decimal, cls=StandardJSONEncoder, indent=2)
print(f"Serialized decimal: {json_output_decimal}")
# Expected output: {"price": "19.99"}