docs: def find_packages(name, pkg_dir):
      """Locate pre-built packages in the _packages directory"""
      for c in (FileSystemPackageBuilder, ZipPackageBuilder, ExcelPackageBuilder):
  
          package_path, cache_path = c.make_package_path(pkg_dir, name)
  
          if package_path.exists():
  
              yield c.type_code, package_path, cache_path