Compute hash for the `file_obj`.

        Attr:
            file_obj (obj): File-like object with ``.write()`` and ``.seek()``.

        Returns:
            str: Hexdigest of the hash.

def _get_hash(self, file_obj):
        """
        Compute hash for the `file_obj`.

        Attr:
            file_obj (obj): File-like object with ``.write()`` and ``.seek()``.

        Returns:
            str: Hexdigest of the hash.
        """
        size = 0
        hash_buider = self.hash_builder()
        for piece in self._get_file_iterator(file_obj):
            hash_buider.update(piece)
            size += len(piece)

        file_obj.seek(0)

        return "%s_%x" % (hash_buider.hexdigest(), size)