docs: def file_containing_import(import_path, import_root):
      '''Finds the file that might contain the import_path.
      '''
      if not _import_paths:
          load_stdlib()
  
      if os.path.isfile(import_root):
          import_root = os.path.dirname(import_root)
  
      search_paths = [import_root] + _import_paths
      module_parts = import_path.split('.')
      for i in range(len(module_parts), 0, -1):
          module_path = os.path.join(*module_parts[:i])
          for sp in search_paths:
              p = os.path.join(sp, module_path)
              if os.path.isdir(p):
                  return os.path.join(p, '__init__.py')
              elif os.path.isfile(p + '.py'):
                  return p + '.py'
      return None