Compute the md5 checksum of a file

def _get_file_md5(filename):
    """Compute the md5 checksum of a file"""
    md5_data = md5()
    with open(filename, 'rb') as f:
        for chunk in iter(lambda: f.read(128*md5_data.block_size), b''):
            md5_data.update(chunk)
    return md5_data.hexdigest()