def __init__(self, path_mapping=None):
    try:
        from petrel_client import client
    except ImportError:
        raise ImportError('Please install petrel_client to enable PetrelBackend.')
    self._client = client.Client()
    assert (isinstance(path_mapping, dict) or (path_mapping is None))
    self.path_mapping = path_mapping
def __init__(self, path_mapping=None):
    try:
        from petrel_client import client
    except ImportError:
        raise ImportError('Please install petrel_client to enable PetrelBackend.')
    self._client = client.Client()
    assert (isinstance(path_mapping, dict) or (path_mapping is None))
    self.path_mapping = path_mapping