Python: Streaming Gzip reader

gzipinputstream.py

import zlib
import string

BLOCK_SIZE = 16384
"""Read block size"""

WINDOW_BUFFER_SIZE = 16 + zlib.MAX_WBITS
"""zlib window buffer size, set to gzip's format"""


class GzipInputStream(object):
    """
    Simple class that allow streaming reads from GZip files.

    Python 2.x gzip.GZipFile relies on .seek() and .tell(), so it
    doesn't support this (@see: http://bo4.me/YKWSsL).

    Adapted from: http://effbot.org/librarybook/zlib-example-4.py
    """

    def __init__(self, fileobj):
        """
        Initialize with the given file-like object.

        @param fileobj: file-like object,
        """
        self._file = fileobj
        self._zip = zlib.decompressobj(WINDOW_BUFFER_SIZE)
        self._offset = 0  # position in unzipped stream
        self._data = ""

    def __fill(self, num_bytes):
        """
        Fill the internal buffer with 'num_bytes' of data.

        @param num_bytes: int, number of bytes to read in (0 = everything)
        """

        if not self._zip:
            return

        while not num_bytes or len(self._data) < num_bytes:
            data = self._file.read(BLOCK_SIZE)
            if not data:
                self._data = self._data + self._zip.flush()
                self._zip = None  # no more data
                break

            self._data = self._data + self._zip.decompress(data)

    def __iter__(self):
        return self

    def seek(self, offset, whence=0):
        if whence == 0:
            position = offset
        elif whence == 1:
            position = self._offset + offset
        else:
            raise IOError("Illegal argument")
        if position < self._offset:
            raise IOError("Cannot seek backwards")

        # skip forward, in blocks
        while position > self._offset:
            if not self.read(min(position - self._offset, BLOCK_SIZE)):
                break

    def tell(self):
        return self._offset

    def read(self, size=0):
        self.__fill(size)
        if size:
            data = self._data[:size]
            self._data = self._data[size:]
        else:
            data = self._data
            self._data = ""
        self._offset = self._offset + len(data)
        return data

    def next(self):
        line = self.readline()
        if not line:
            raise StopIteration()
        return line

    def readline(self):
        # make sure we have an entire line
        while self._zip and "\n" not in self._data:
            self.__fill(len(self._data) + 512)

        pos = string.find(self._data, "\n") + 1
        if pos <= 0:
            return self.read()
        return self.read(pos)

    def readlines(self):
        lines = []
        while True:
            line = self.readline()
            if not line:
                break
            lines.append(line)
        return lines

Have an example on use case?

any working example ?