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