'Initializes this instance with the given blob key and file range.
This BlobstoreZipInputReader will read from the file with index start_index
up to but not including the file with index end_index.
Args:
blob_key: the BlobKey that this input reader is processing.
start_index: the index of the first file to read.
end_index: the index of the first file that will not be read.
_reader: a callable that returns a file-like object for reading blobs.
Used for dependency injection.'

def __init__(self, blob_key, start_index, end_index, _reader=blobstore.BlobReader):

    self._blob_key = blob_key
    self._start_index = start_index
    self._end_index = end_index
    self._reader = _reader
    self._zip = None
    self._entries = None
