def readChunk(offset, length):
        """
        Read from the file.

        If EOF is reached before any data is read, raise EOFError.

        This method returns the data as a string, or a Deferred that is
        called back with same.

        @param offset: an integer that is the index to start from in the file.
        @param length: the maximum length of data to return.  The actual amount
        returned may less than this.  For normal disk files, however,
        this should read the requested number (up to the end of the file).
        """

        Read from the file.

        If EOF is reached before any data is read, raise EOFError.

        This method returns the data as a string, or a Deferred that is
        called back with same.

        @param offset: an integer that is the index to start from in the file.
        @param length: the maximum length of data to return.  The actual amount
        returned may less than this.  For normal disk files, however,
        this should read the requested number (up to the end of the file).
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/interfaces.py