packaging 26.3: Parse PEP 508 environment markers and evaluate them against environment dictionaries with boolean logic and extra normalization using packaging.markers

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: Parse PEP 508 environment markers and evaluate them against environment dictionaries with boolean logic and extra normalization using packaging.markers
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:pypi/packaging@26.3
Demonstrate these symbols/APIs:
  - packaging.markers.InvalidMarker
  - packaging.markers.Marker
  - packaging.markers.default_environment

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:c08ec3fdac3b6fa92550b9dde39a580ade33c4c69894cbfc983cb1c8a3d2b467","contract":["parse PEP 508 environment markers with boolean operators and version comparisons","evaluate markers against custom environment dictionaries overriding os and python version","evaluate markers against the runtime default environment","match extras with automatic canonicalization of hyphens and underscores","raise InvalidMarker on malformed expressions or invalid marker variable names"],"goal":"Parse PEP 508 environment markers and evaluate them against environment dictionaries with boolean logic and extra normalization using packaging.markers","kind":"HOW","packages":["pkg:pypi/packaging@26.3"],"schemaVersion":1,"symbols":["packaging.markers.InvalidMarker","packaging.markers.Marker","packaging.markers.default_environment"]},"contractCommand":["python","test/contract.py"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"pypi","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"pip","schemaVersion":1},"license":"MIT-0","packages":["pkg:pypi/packaging@26.3"],"schemaVersion":1,"subject":"pkg:pypi/packaging@26.3","symbols":["packaging.markers.InvalidMarker","packaging.markers.Marker","packaging.markers.default_environment"],"verifierAdapter":"python@1"}

packaging==26.3

{
  "schemaVersion": 1,
  "goal": "Parse PEP 508 environment markers and evaluate them against environment dictionaries with boolean logic and extra normalization using packaging.markers",
  "kind": "HOW",
  "packages": [
    "pkg:pypi/packaging@26.3"
  ],
  "symbols": [
    "packaging.markers.InvalidMarker",
    "packaging.markers.Marker",
    "packaging.markers.default_environment"
  ]
}

"""PEP 508 environment marker parsing and evaluation utilities."""

"""PEP 508 environment marker parsing and evaluation using packaging.markers."""

from collections.abc import Mapping
from packaging.markers import InvalidMarker, Marker, default_environment


def parse_marker(marker_expr: str) -> Marker:
    """Parse a PEP 508 marker expression.

    Raises InvalidMarker if syntax is invalid or references unknown marker variables.
    """
    return Marker(marker_expr)


def is_marker_valid(marker_expr: str) -> bool:
    """Check if a marker expression is syntactically valid according to PEP 508."""
    try:
        Marker(marker_expr)
        return True
    except InvalidMarker:
        return False


def evaluate_marker(
    marker_expr: str,
    environment: Mapping[str, str] | None = None,
) -> bool:
    """Evaluate a marker expression against an environment mapping.

    If environment is None, the runtime default environment is used.
    """
    marker = Marker(marker_expr)
    return marker.evaluate(environment)


def evaluate_with_extra(marker_expr: str, extra: str) -> bool:
    """Evaluate a marker with an active extra, canonicalizing name per PEP 685."""
    marker = Marker(marker_expr)
    return marker.evaluate({"extra": extra})


def get_system_marker_environment() -> dict[str, str]:
    """Return the default environment dictionary detected from the running process."""
    return default_environment()

import os
import sys

sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
from packaging.markers import InvalidMarker
from src.marker_evaluator import (
    evaluate_marker,
    evaluate_with_extra,
    get_system_marker_environment,
    is_marker_valid,
    parse_marker,
)

# 1. Parse and evaluate compound marker with boolean operators and version comparisons
marker = parse_marker("python_version >= '3.8' and (os_name == 'posix' or sys_platform == 'linux')")
assert str(marker) == 'python_version >= "3.8" and (os_name == "posix" or sys_platform == "linux")'

# 2. Evaluate against custom environment dictionaries overriding os and python version
posix_env = {"python_version": "3.11", "os_name": "posix", "sys_platform": "darwin"}
assert evaluate_marker("python_version >= '3.8' and os_name == 'posix'", posix_env) is True

win_env = {"python_version": "3.11", "os_name": "nt", "sys_platform": "win32"}
assert evaluate_marker("python_version >= '3.8' and os_name == 'posix'", win_env) is False

old_py_env = {"python_version": "3.7", "os_name": "posix", "sys_platform": "darwin"}
assert evaluate_marker("python_version >= '3.8' and os_name == 'posix'", old_py_env) is False

# 'in' and 'not in' operators
assert evaluate_marker("sys_platform in 'linux, darwin'", posix_env) is True
assert evaluate_marker("sys_platform in 'linux, darwin'", win_env) is False

# 3. Evaluate markers against runtime default environment
system_env = get_system_marker_environment()
assert "python_version" in system_env
assert "sys_platform" in system_env
assert "os_name" in system_env
assert evaluate_marker(f"os_name == '{system_env['os_name']}'") is True

# 4. Match extras with automatic canonicalization of hyphens and underscores (PEP 685)
assert evaluate_with_extra("extra == 'secure-socks'", "secure_socks") is True
assert evaluate_with_extra("extra == 'secure_socks'", "secure-socks") is True
assert evaluate_with_extra("extra == 'secure-socks'", "other") is False

# 5. InvalidMarker error handling for syntax errors and unknown marker variable names
assert is_marker_valid("python_version >= '3.8'") is True
assert is_marker_valid("python_version >> '3.8'") is False
assert is_marker_valid("unknown_var == 'value'") is False
assert is_marker_valid("") is False

try:
    parse_marker("unknown_marker_var == '1.0'")
    assert False, "Should have raised InvalidMarker"
except InvalidMarker:
    pass

print("CONTRACT PASS: packaging markers parsed, validated, and evaluated correctly")