scjson 0.1.5

A JSON-based serialization of SCXML (State Chart XML) for modern tooling, interoperability, and education.

scjson Python Package

This directory contains the Python implementation of scjson, a format for representing SCXML state machines in JSON. The package provides a command line interface and utility functions to convert between .scxml and .scjson files and to validate documents against the project's schema.

Installation

pip install scjson

You can also install from a checkout of this repository:

cd py && pip install -e .

Source Code - Multi-Language Support

[https://github.com/SoftOboros/scjson/]

• csharp
• go
• java
• javascript / typescript
• lua
• python
• ruby
• rust
• swift

Command Line Usage

After installation the scjson command is available:

# Convert a single file
scjson json path/to/machine.scxml

# Convert back to SCXML
scjson xml path/to/machine.scjson

# Validate recursively
scjson validate path/to/dir -r

FastAPI example Usage

This is a minimal FastAPI endpoint as an example usage of the SCXMLDocumentHandler class.

import json
from fastapi import FastAPI, Request, HTTPException, Response
from scjson.SCXMLDocumentHandler import SCXMLDocumentHandler

app = FastAPI()
handler = SCXMLDocumentHandler(schema_path=None)

# In-memory store for demo
store = {}

@app.get("/xml/{slug}")
async def get_xml(slug: str):
    """Return the SCXML document as XML."""
    data = store.get(slug)
    if not data:
        raise HTTPException(status_code=404, detail="Document not found")
    xml_str = handler.json_to_xml(json.dumps(data))
    return Response(content=xml_str, media_type="application/xml")

@app.post("/xml/{slug}")
async def post_xml(slug: str, request: Request):
    """Accept an SCXML document and convert it to scjson."""
    xml_bytes = await request.body()
    xml_str = xml_bytes.decode("utf-8")
    json_str = handler.xml_to_json(xml_str)
    data = json.loads(json_str)
    data.setdefault("name", slug)
    store[slug] = data
    return data

SCJSON Caveats

The SCXML conversion helpers normalize data so it can be stored as JSON. During asdict() serialization the generated dataclasses may contain Decimal values and enumeration instances (e.g. AssignTypeDatatype).

• Decimal values are converted to floating point numbers.
• Enum values are stored using their .value string.

These conversions allow the JSON representation to be serialized by json.dumps and then converted back via the _to_dataclass helper.

Model Variants

The Python package exposes four sets of generated models that mirror the SCJSON schema. They all share the same field names and enumerations, but offer different runtime characteristics.

Enums

Each enumeration represents a restricted string set used by SCXML. The values shown below mirror those defined in the SCJSON schema.

• AssignTypeDatatype – how the <assign> element manipulates the datamodel. Values: replacechildren, firstchild, lastchild, previoussibling, nextsibling, replace, delete, addattribute.
• BindingDatatype – determines if datamodel variables are bound early or late during execution.
• BooleanDatatype – boolean attribute values true or false.
• ExmodeDatatype – processor execution mode, either lax or strict.
• HistoryTypeDatatype – type of <history> state: shallow or deep.
• TransitionTypeDatatype – whether a <transition> is internal or external.

Common Types

Several generated classes share generic helper fields:

• other_attributes: dict[str, str] capturing additional XML attributes from foreign namespaces.
• other_element: list[object] allowing untyped child nodes from other namespaces to be preserved.
• content: list[object] used when elements permit mixed or wildcard content.

scjson.dataclasses

Plain Python dataclasses without runtime validation.

• Assign – update a datamodel location with an expression or value.
• Cancel – cancel a pending <send> operation.
• Content – inline payload used by <send> and <invoke>.
• Data – represents a single datamodel variable.
• Datamodel – container for one or more <data> elements.
• Donedata – payload returned when a <final> state is reached.
• Else – fallback branch for <if> conditions.
• Elseif – conditional branch following an <if>.
• Final – marks a terminal state in the machine.
• Finalize – executed after an <invoke> completes.
• Foreach – iterate over items within executable content.
• History – pseudostate remembering previous active children.
• If – conditional execution block.
• Initial – starting state within a compound state.
• Invoke – run an external process or machine.
• Log – diagnostic output statement.
• Onentry – actions performed when entering a state.
• Onexit – actions performed when leaving a state.
• Parallel – coordinates concurrent regions.
• Param – parameter passed to <invoke> or <send>.
• Raise – raise an internal event.
• Script – inline executable script.
• Scxml – root element of an SCJSON document.
• Send – dispatch an external event.
• State – basic state node.
• Transition – edge between states triggered by events.

scjson.dataclasses_strict

The same dataclasses as above but configured for stricter type checking.

scjson.pydantic

Pydantic BaseModel classes generated from the SCJSON schema. They provide data validation and convenient .model_dump() helpers.

scjson.pydantic_strict

Pydantic models with strict validation settings.

License

All source code in this directory is released under the BSD 1-Clause license. See LICENSE and LEGAL.md for details.