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/.

Rule Engine expressions are written in their own language, defined as strings in Python. Some features of this language includes:

• Optional type hinting
• Matching strings with regular expressions
• Datetime datatypes
• Data attributes

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': '[email protected]'
}) # => True
rule.matches({
   'first_name': 'Darth', 'last_name': 'Vader', 'email': '[email protected]'
}) # => 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.

• Spencer McIntyre - zeroSteiner (@zeroSteiner)