import zlib


def crc32File(filename, skip=0):
    """Computes the CRC-32 of the contents of filename, optionally
    skipping a certain number of bytes at the beginning of the file.
    """
    with open(filename, 'rb') as stream:
        discard = stream.read(skip)
        return zlib.crc32(stream.read()) & 0xffffffff