dataweave-py 0.4.0

DataWeave interpreter running natively on Python

DataWeave-Py

A native Python implementation of the DataWeave data transformation language, providing powerful data transformation capabilities directly in Python without requiring the JVM.

Install from PyPI:

uv add dataweave-py

or

pip install dataweave-py

DataWeave Playground

For the best DataWeave Playground a without payload size limits DataWeave Playground, visit: https://dataweavelang.org

Optional extras:

# pandas helpers (DataFrame/Series input normalization)
pip install "dataweave-py[pandas]"

# pydantic helpers
pip install "dataweave-py[pydantic]"

# everything
pip install "dataweave-py[full]"

Overview

DataWeave-Py (dwpy) is a Python interpreter for the DataWeave language, originally developed by MuleSoft for data transformation in the Mule runtime. This project brings DataWeave's expressive transformation syntax and rich feature set to the Python ecosystem, enabling:

• Data transformation: Convert between JSON, XML, CSV and other formats
• Functional programming: Leverage map, filter, reduce, and other functional operators
• Pattern matching: Use powerful match expressions with guards and bindings
• Safe navigation: Handle null values gracefully with null-safe operators
• Rich built-ins: Access 100+ built-in functions for strings, numbers, dates, arrays, and objects

Requirements

• Python 3.10 or higher
• Dependencies managed via uv (recommended) or pip

Quick Start

Basic Usage

from dwpy import DataWeaveRuntime

# Create a runtime instance
runtime = DataWeaveRuntime()

# Define a DataWeave script
script = """%dw 2.0
output application/json
---
{
  message: "Hello, " ++ upper(payload.name),
  timestamp: now()
}
"""

# Execute with a payload
payload = {"name": "world"}
result = runtime.execute(script, payload)

print(result)
# Output: {'message': 'Hello, WORLD', 'timestamp': '2025-11-03T...Z'}

Data Transformation Example

from dwpy import DataWeaveRuntime

runtime = DataWeaveRuntime()

# Transform and enrich order data
script = """%dw 2.0
output application/json
---
{
  orderId: payload.id,
  status: upper(payload.status default "pending"),
  total: payload.items reduce ((item, acc = 0) -> 
    acc + (item.price * (item.quantity default 1))
  ),
  itemCount: sizeOf(payload.items)
}
"""

payload = {
    "id": "ORD-123",
    "status": "confirmed",
    "items": [
        {"price": 29.99, "quantity": 2},
        {"price": 15.50, "quantity": 1}
    ]
}

result = runtime.execute(script, payload)
print(result)
# Output: {'orderId': 'ORD-123', 'status': 'CONFIRMED', 'total': 75.48, 'itemCount': 2}

Using Variables

from dwpy import DataWeaveRuntime

runtime = DataWeaveRuntime()

script = """%dw 2.0
output application/json
var requestTime = vars.requestTime default now()
---
{
  user: payload.userId,
  processedAt: requestTime
}
"""

payload = {"userId": "U-456"}
vars = {"requestTime": "2024-05-05T12:00:00Z"}

result = runtime.execute(script, payload, vars=vars)

Pattern Matching

from dwpy import DataWeaveRuntime

runtime = DataWeaveRuntime()

script = """%dw 2.0
output application/json
---
{
  category: payload.price match {
    case var p when p > 100 -> "premium",
    case var p when p > 50 -> "standard",
    else -> "budget"
  }
}
"""

result = runtime.execute(script, {"price": 75})
# Output: {'category': 'standard'}

String Interpolation

from dwpy import DataWeaveRuntime

runtime = DataWeaveRuntime()

# Simple interpolation
script = """%dw 2.0
output application/json
---
{
  greeting: "Hello $(payload.name)!",
  total: "Total: $(payload.price * payload.quantity)",
  status: "Order $(payload.orderId) is $(upper(payload.status))"
}
"""

payload = {
    "name": "Alice",
    "price": 10.5,
    "quantity": 3,
    "orderId": "ORD-123",
    "status": "confirmed"
}

result = runtime.execute(script, payload)
# Output: {
#   'greeting': 'Hello Alice!',
#   'total': 'Total: 31.5',
#   'status': 'Order ORD-123 is CONFIRMED'
# }

String interpolation allows you to embed expressions directly within strings using the $(expression) syntax. The expression can be:

• Property access: $(payload.name)
• Nested properties: $(payload.user.email)
• Expressions: $(payload.price * 1.1)
• Function calls: $(upper(payload.status))
• Any valid DataWeave expression

Output Formats

The runtime supports these output directives:

• application/python (native Python objects)
• application/json
• application/csv
• application/xml
• text/plain
• text/markdown

Format-specific notes:

• output text/plain only works when the final script result is a string.
• output text/markdown expects a tabular value (list or dict) and renders a Markdown table.
• output text/markdown header=false is rejected because Markdown table rendering requires headers.
• payload_format="text/markdown" parses Markdown pipe tables into structured rows (Array<Object> by default, or Array<Array<String>> with payload_format_options={"header": False}).

Supported Features

DataWeave-Py currently supports a wide range of DataWeave language features:

Core Language Features

• ✅ Header directives (%dw 2.0, output, var, import)
• ✅ Payload and variable access
• ✅ Object and array literals
• ✅ Field selectors (.field, ?.field, [index])
• ✅ Comments (line // and block /* */)
• ✅ Default values (payload.field default "fallback")
• ✅ String interpolation ("Hello $(payload.name)")

Operators

• ✅ Concatenation (++)
• ✅ Difference (--)
• ✅ Arithmetic (+, -, *, /)
• ✅ Comparison (==, !=, >, <, >=, <=)
• ✅ Logical (and, or, not)
• ✅ Range (to)

Control Flow

• ✅ Conditional expressions (if-else)
• ✅ Pattern matching (match-case)
• ✅ Match guards (case var x when condition)

Collection Operations

• ✅ map - Transform elements
• ✅ filter - Select elements
• ✅ reduce - Aggregate values
• ✅ flatMap - Map and flatten
• ✅ distinctBy - Remove duplicates
• ✅ groupBy - Group by criteria
• ✅ orderBy - Sort elements

Built-in Functions

String Functions

upper, lower, trim, contains, startsWith, endsWith, isBlank, splitBy, joinBy, find, match, matches

Numeric Functions

abs, ceil, floor, round, pow, mod, sum, avg, max, min, random, randomInt, isDecimal, isInteger, isEven, isOdd

Array/Object Functions

sizeOf, isEmpty, flatten, indexOf, lastIndexOf, distinctBy, filterObject, keysOf, valuesOf, entriesOf, pluck, maxBy, minBy

Date Functions

now, isLeapYear, daysBetween

Utility Functions

log, logInfo, logDebug, logWarn, logError

Running Tests

The project includes comprehensive test coverage:

# Run all tests
pytest

# Run specific test file
pytest tests/test_runtime_basic.py

# Run with verbose output
pytest -v

# Run with coverage
pytest --cov=dwpy

Browser WASM (Pyodide)

The project includes a browser-worker runtime for WASM execution with Pyodide and wheel-based loading.

• Worker bootstrap: web/pyodide-worker.mjs
• Python entrypoint: dwpy.wasm_entry.run_dataweave(...)
• Full instructions: docs/WASM_PYODIDE.md

Language Server (LSP)

The project now includes a stdio Language Server for DataWeave:

• Command: dwpy-lsp
• Module: dwpy.lsp.server
• Engine shared with Monaco + WASM completion bridge: dwpy.lsp.engine

Install

Install the LSP extra:

uv pip install "dataweave-py[lsp]"

Sidecar context files

For structure-aware payload/vars completion in .dwl files, place these JSON files next to the script:

• <file>.payload.json
• <file>.vars.json

Example for transform.dwl:

• transform.dwl.payload.json
• transform.dwl.vars.json

If sidecars are missing or invalid, the server falls back to script-only inference.

VS Code client (example)

{
  "languageserver": {
    "dataweave-py": {
      "command": "dwpy-lsp",
      "filetypes": ["dataweave", "dwl"]
    }
  }
}

Neovim client (example)

require("lspconfig").dwpy_lsp.setup({
  cmd = { "dwpy-lsp" },
  filetypes = { "dataweave", "dwl" },
})

Project Structure

runtime-2.11.0-20250825-src/
├── dwpy/                      # Main Python package
│   ├── __init__.py           # Package exports
│   ├── parser.py             # DataWeave parser
│   ├── runtime.py            # Execution engine
│   └── builtins.py           # Built-in functions
├── tests/                     # Test suite
│   ├── test_runtime_basic.py # Core functionality tests
│   ├── test_builtins.py      # Built-in function tests
│   └── fixtures/             # Test data and fixtures
├── runtime-2.11.0-20250825/  # Original JVM runtime reference
├── docs/                      # Documentation
├── pyproject.toml            # Project configuration
└── README.md                 # This file

Development

Setting Up Development Environment

# Create virtual environment
uv venv --python 3.12
source .venv/bin/activate

# Install development dependencies
uv pip sync

# Install in editable mode
pip install -e .

Running the Test Suite

# Run all tests
python -m pytest tests/

# Run specific test category
python -m pytest tests/test_builtins.py

# Run with coverage report
python -m pytest --cov=dwpy --cov-report=html tests/

Code Style

The project follows standard Python conventions:

• PEP 8 style guide
• Type hints where appropriate
• Comprehensive docstrings
• Two-space indentation for consistency with Scala codebase

Comparison with JVM Runtime

DataWeave-Py aims to provide feature parity with the official JVM-based DataWeave runtime. Key differences:

Feature	JVM Runtime	DataWeave-Py
Language	Scala	Python
Performance	High (compiled)	Good (interpreted)
Startup Time	Slower (JVM warmup)	Fast (native Python)
Memory Usage	Higher (JVM overhead)	Lower (Python runtime)
Integration	Java/Mule apps	Python apps
Module System	Full support	In progress
Type System	Static typing	Dynamic typing

Roadmap

Current Status (v0.1.0)

• ✅ Core language parser
• ✅ Expression evaluation
• ✅ 60+ built-in functions
• ✅ Pattern matching
• ✅ Collection operators

Planned Features

• 🔄 Full module system support
• 🔄 Import statements
• 🔄 Custom function definitions
• 🔄 XML/CSV format support
• 🔄 Streaming for large datasets
• 🔄 Type validation
• 🔄 Performance optimizations

Contributing

Contributions are welcome! Please:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Write tests for your changes
4. Ensure all tests pass (pytest)
5. Commit your changes (git commit -m 'feat: add amazing feature')
6. Push to the branch (git push origin feature/amazing-feature)
7. Open a Pull Request

License

See the original DataWeave runtime license terms. This project is a reference implementation for educational and development purposes.

Resources

• DataWeave Documentation
• DataWeave Tutorial
• DataWeave Playground

Support

For questions, issues, or contributions:

• Open an issue on GitHub
• Check existing documentation in the docs/ directory
• Review test cases in tests/ for usage examples

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Note: This is an independent Python implementation and is not officially supported by MuleSoft. For production use cases requiring full DataWeave compatibility, please use the official JVM-based runtime.