Fast, Safe, and Expressive evaluation of Google's Common Expression Language (CEL) in Python, powered by Rust.
The Common Expression Language (CEL) is a non-Turing complete language designed for simplicity, speed, and safety. This Python package wraps the Rust implementation cel-interpreter v0.10.0, providing microsecond-level expression evaluation with seamless Python integration.
- 🛡️ Policy Enforcement: Define access control rules that can be updated without code changes
- ⚙️ Configuration Validation: Validate complex settings with declarative rules
- 🔄 Data Transformation: Transform and filter data with safe, portable expressions
- 📋 Business Rules: Implement decision logic that business users can understand
- 🔍 Query Filtering: Build dynamic filters for databases and APIs
- 🎯 Feature Flags: Create sophisticated feature toggle conditions
pip install common-expression-languageOr using uv:
uv add common-expression-languageAfter installation, both the Python library and the cel command-line tool will be available.
📖 Full Documentation: https://python-common-expression-language.readthedocs.io/
from cel import evaluate
# Simple expressions
result = evaluate("1 + 2") # 3
result = evaluate("'Hello ' + 'World'") # "Hello World"
result = evaluate("age >= 18", {"age": 25}) # True
# Complex expressions with context
result = evaluate(
'user.role == "admin" && "write" in permissions',
{
"user": {"role": "admin"},
"permissions": ["read", "write", "delete"]
}
) # True# Simple evaluation
cel '1 + 2' # 3
# With context
cel 'age >= 18' --context '{"age": 25}' # true
# Interactive REPL
cel --interactivefrom cel import Context, evaluate
def calculate_discount(price, rate):
return price * rate
context = Context()
context.add_function("calculate_discount", calculate_discount)
context.add_variable("price", 100)
result = evaluate("price - calculate_discount(price, 0.1)", context) # 90.0from cel import evaluate, Context
# Access control policy
policy = """
user.role == "admin" ||
(resource.owner == user.id && current_hour >= 9 && current_hour <= 17)
"""
context = Context()
context.update({
"user": {"id": "alice", "role": "user"},
"resource": {"owner": "alice"},
"current_hour": 14 # 2 PM
})
access_granted = evaluate(policy, context) # True- ✅ Fast Evaluation: Microsecond-level expression evaluation via Rust
- ✅ Rich Type System: Integers, floats, strings, lists, maps, timestamps, durations
- ✅ Python Integration: Seamless type conversion and custom function support
- ✅ CLI Tools: Interactive REPL and batch processing capabilities
- ✅ Safety First: Non-Turing complete, safe for untrusted expressions
📚 Complete documentation available at: https://python-common-expression-language.readthedocs.io/
To build and serve the documentation locally:
# Install documentation dependencies
uv sync --group docs
# Build the documentation
uv run --group docs mkdocs build
# Serve locally with live reload
uv run --group docs mkdocs serveThe documentation will be available at http://localhost:8000
# Run all tests
uv run pytest
# Run with coverage
uv run pytest --cov=cel
# Test all documentation examples (embedded code + standalone files)
uv run --group docs pytest tests/test_docs.py -v# Install development dependencies
uv sync --dev
# Build the package
uv run maturin develop
# Run tests
uv run pytestContributions are welcome! Please see our documentation for:
- CEL compliance status
- Development setup and guidelines
- Areas where help is needed
This project is licensed under the same terms as the original cel-interpreter crate.