Function resolvePythonVersion

packages/python/src/version.ts:189–322

({
  isDev,
  pythonPackage,
  rootDir,
}: {
  isDev?: boolean;
  pythonPackage: PythonPackage;
  rootDir: string;
})

 * logging, warnings, and error handling.
 */
export function resolvePythonVersion({
  isDev,
  pythonPackage,
  rootDir,
}: {
  isDev?: boolean;
  pythonPackage: PythonPackage;
  rootDir: string;
}): PythonVersionResolution {
  if (isDev) {
    return {
      pythonVersion: getDevPythonVersion(),
      pythonPackage,
    };
  }

  const constraints = pythonPackage.requiresPython;
  const defaultPv = getDefaultPythonVersion({ isDev: false });

  let selection: PythonVersion;
  let source: string | undefined;
  let autoUpgraded = false;

  if (!constraints || constraints.length === 0) {
    console.log(
      `No Python version specified in .python-version, pyproject.toml, or Pipfile.lock. Using python version: ${pythonVersionString(defaultPv)}`
    );
    selection = defaultPv;
  } else {
    const defaultBuild = toPythonBuild(defaultPv);
    const availableBuilds = getAvailablePythonBuilds();
    const allBuilds = getAllPythonBuilds();

    const result = selectPythonVersion({
      constraints,
      availableBuilds,
      allBuilds,
      defaultBuild,
      majorMinorOnly: true,
      legacyTildeEquals: true,
    });

    source = result.source;
    selection = getPythonVersionForBuild(result.build) ?? defaultPv;

    // Auto-upgrade: when the constraint comes from a converted manifest
    // (e.g. Pipfile.lock) and resolves to a version below the default,
    // upgrade to the default.  Legacy projects often pin old versions
    // that are incompatible with the builder's runtime requirements.
    if (
      pythonPackage.manifest?.origin &&
      !result.notAvailable &&
      !result.invalidConstraint &&
      !versionLessOrEqual(defaultPv, selection)
    ) {
      const originalVersion = pythonVersionString(selection);
      selection = defaultPv;
      autoUpgraded = true;