Source code for duplicity.filechunkio

# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4; encoding:utf-8 -*-
# Copyright 2011 Fabian Topfstedt <>
# This module is included with granted permission from the original author.
# The original source is available at

import io
import os

SEEK_SET = getattr(io, "SEEK_SET", 0)
SEEK_CUR = getattr(io, "SEEK_CUR", 1)
SEEK_END = getattr(io, "SEEK_END", 2)

[docs]class FileChunkIO(io.FileIO): """ A class that allows you reading only a chunk of a file. """
[docs] def __init__( self, name, mode="r", closefd=True, offset=0, bytes=None, *args, **kwargs # pylint: disable=redefined-builtin ): # pylint: disable=redefined-builtin """ Open a file chunk. The mode can only be 'r' for reading. Offset is the amount of bytes that the chunks starts after the real file's first byte. Bytes defines the amount of bytes the chunk has, which you can set to None to include the last byte of the real file. """ if not mode.startswith("r"): raise ValueError("Mode string must begin with 'r'") self.offset = offset self.bytes = bytes if bytes is None: self.bytes = os.stat(name).st_size - self.offset super().__init__(os.fsdecode(name), mode, closefd, *args, **kwargs)
[docs] def seek(self, offset, whence=SEEK_SET): """ Move to a new chunk position. """ if whence == SEEK_SET: super().seek(self.offset + offset) elif whence == SEEK_CUR: + offset) elif whence == SEEK_END: + offset)
[docs] def tell(self): """ Current file position. """ return super().tell() - self.offset
[docs] def read(self, n=-1): """ Read and return at most n bytes. """ if n >= 0: max_n = self.bytes - self.tell() n = min([n, max_n]) return super().read(n) else: return self.readall()
[docs] def readall(self): """ Read all data from the chunk. """ return - self.tell())
[docs] def readinto(self, b): """ Same as RawIOBase.readinto(). """ data = n = len(data) try: b[:n] = data except TypeError as err: import array if not isinstance(b, array.array): raise err b[:n] = array.array(b"b", data) return n