rule-engine

library5.0.0pypiunverified

rule-engine is a lightweight, optionally typed expression language with a custom grammar for matching arbitrary Python objects. It provides a simple way to define and evaluate complex rules against data, supporting various data types and custom functions. The current stable version is 4.5.3, with frequent patch releases and a v5 alpha in active development.

serialization data

pip install rule-engine

INSTALL

IMPORT

SIG · RULE-ENGINE

rule-engine

serializationenv5.0.0

Install

1.8s avg

Import

616ms

Disk

18MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v5.0.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.910 runs

installs and imports cleanly · install 0.0s · import 0.641s · 19.6MB

glibc

py 3.10–3.910 runs

installs and imports cleanly · install 1.8s · import 0.590s · 20MB

18MB installed

● package 18MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

Rule

✓ from rule_engine import Rule

Context

✓ from rule_engine import Context

Used for advanced scenarios like custom functions or type definitions.

DataType

✓ from rule_engine import DataType

Essential when defining custom data types or explicit type coercions.

This quickstart demonstrates how to create a `Rule` instance with an expression string and then evaluate it against a Python dictionary acting as the data context. The rule expression uses built-in functions like `sum` and logical operators.

from rule_engine import Rule # Define a rule with an expression string rule = Rule('sum(items) > 100 && "apple" in items') # Evaluate the rule against different data contexts print(f"Result 1: {rule.matches({'items': [10, 20, 30, 40, 50, "apple"]})})") print(f"Result 2: {rule.matches({'items': [10, 20, "orange"]})})")

Debug

Known issues

breakingVersion 5.0.0 is in alpha (v5.0.0a1 has been released) and introduces significant breaking changes and API refactors. Do not update to v5.x without thoroughly reviewing the changelog and migrating your code.

fix

Pin your dependency to `rule-engine<5.0.0` to avoid accidental upgrades. Consult the v5 changelog when you're ready to migrate.

affects: All versions prior to 5.0.0

gotchaFrom v4.5.0 onwards, rule-engine is stricter about invalid string literals and function return types. `StringSyntaxError` is now raised for malformed string literals and `FunctionCallError` for type-incompatible function returns, where previous versions might have had different behavior.

fix

Ensure string literals are correctly formatted and custom functions return values compatible with their declared `DataType`.

affects: >=4.5.0

gotchaThe backslash character (`\`) is used for escaping in rule strings. If you need a literal backslash in your rule (e.g., in a regex pattern or string literal), you must double-escape it (e.g., `\\`).

fix

Escape literal backslashes by doubling them: `"\\"` in the rule string to represent a single backslash.

affects: All versions

gotchaWhen defining custom functions or interacting with complex Python objects, ensure you correctly use `Context` and `DataType` objects. Incorrect type declarations or context setup can lead to unexpected `FunctionCallError` or evaluation issues.

fix

Refer to the official documentation on `Context` and `DataType` for defining custom functions and managing evaluation environments effectively.

affects: All versions

Upgrade

Version history

5.0.0latest on PyPI · released May 17, 2026

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