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Rule Engine

GitHub Workflow Status (branch) PyPI

A lightweight, optionally typed expression language with a custom grammar for matching arbitrary Python objects.

Documentation is available at https://zeroSteiner.github.io/rule-engine/.

Warning:The next major version (5.0) will remove support Python versions 3.6 and 3.7. There is currently no timeline for its release.

Rule Engine expressions are written in their own language, defined as strings in Python. The syntax is most similar to Python with some inspiration from Ruby. Some features of this language includes:

  • Optional type hinting
  • Matching strings with regular expressions
  • Datetime datatypes
  • Compound datatypes (equivalents for Python dict, list and set types)
  • Data attributes
  • Thread safety

Example Usage

The following example demonstrates the basic usage of defining a rule object and applying it to two dictionaries, showing that one matches while the other does not. See Getting Started for more information.

import rule_engine
# match a literal first name and applying a regex to the email
rule = rule_engine.Rule(
    'first_name == "Luke" and email =~ ".*@rebels.org$"'
) # => <Rule text='first_name == "Luke" and email =~ ".*@rebels.org$"' >
rule.matches({
    'first_name': 'Luke', 'last_name': 'Skywalker', 'email': 'luke@rebels.org'
}) # => True
rule.matches({
   'first_name': 'Darth', 'last_name': 'Vader', 'email': 'dvader@empire.net'
}) # => False

The next example demonstrates the optional type system. A custom context is created that defines two symbols, one string and one float. Because symbols are defined, an exception will be raised if an unknown symbol is specified or an invalid operation is used. See Type Hinting for more information.

import rule_engine
# define the custom context with two symbols
context = rule_engine.Context(type_resolver=rule_engine.type_resolver_from_dict({
    'first_name': rule_engine.DataType.STRING,
    'age': rule_engine.DataType.FLOAT
}))

# receive an error when an unknown symbol is used
rule = rule_engine.Rule('last_name == "Vader"', context=context)
# => SymbolResolutionError: last_name

# receive an error when an invalid operation is used
rule = rule_engine.Rule('first_name + 1', context=context)
# => EvaluationError: data type mismatch

Want to give the rule expression language a try? Checkout the Debug REPL that makes experimentation easy. After installing just run python -m rule_engine.debug_repl.

Installation

Install the latest release from PyPi using pip install rule-engine. Releases follow Semantic Versioning to indicate in each new version whether it fixes bugs, adds features or breaks backwards compatibility. See the Change Log for a curated list of changes.

Credits

  • Spencer McIntyre - zeroSteiner GitHub followers

License

The Rule Engine library is released under the BSD 3-Clause license. It is able to be used for both commercial and private purposes. For more information, see the LICENSE file.