CHUNK_SIZE = 16 * 8192
class GzipFile(gzip.GzipFile):
    "Version of GzipFile with larger read sizes and thus faster seeks."
    def seek(self, offset, whence=0):
        if whence:
            if whence == 1:
                offset = self.offset + offset
            else:
                raise ValueError('Seek from end not supported')
        if self.mode == gzip.WRITE:
            if offset < self.offset:
                raise IOError('Negative seek in write mode')
            count = offset - self.offset
            for i in xrange(count // CHUNK_SIZE):
                self.write(CHUNK_SIZE * '\0')
            self.write((count % CHUNK_SIZE) * '\0')
        elif self.mode == gzip.READ:
            if offset < self.offset:
                # for negative seek, rewind and do positive seek
                self.rewind()
            count = offset - self.offset
            for i in xrange(count // CHUNK_SIZE):
                self.read(CHUNK_SIZE)
            self.read(count % CHUNK_SIZE)

        return self.offset

    def read(self, size=-1):
        self._check_closed()
        if self.mode != gzip.READ:
            import errno
            raise IOError(errno.EBADF, "read() on write-only GzipFile object")

        if self.extrasize <= 0 and self.fileobj is None:
            return ''

        readsize = CHUNK_SIZE
        if size < 0:        # get the whole thing
            try:
                while True:
                    self._read(readsize)
                    readsize = min(self.max_read_chunk, readsize * 2)
            except EOFError:
                size = self.extrasize
        else:               # just get some more of it
            try:
                while size > self.extrasize:
                    self._read(readsize)
                    readsize = min(self.max_read_chunk, readsize * 2)
            except EOFError:
                if size > self.extrasize:
                    size = self.extrasize

        offset = self.offset - self.extrastart
        chunk = self.extrabuf[offset: offset + size]
        self.extrasize = self.extrasize - size

        self.offset += size
        return chunk