PKCS#7 pad/unpad routines for Python 3

def pkcs7_pad(data, blocksize=16):
    padlen = blocksize - len(data) % blocksize
    return data + bytes([padlen]) * padlen


def pkcs7_unpad(data, blocksize=16):
    if data:
        padlen = data[-1]
        if 0 < padlen < blocksize:
            if data.endswith(bytes([padlen]) * padlen):
                return data[:-padlen]

    raise ValueError('incorrect padding')


if __name__ == '__main__':
    #~ import pdb; pdb.set_trace()
    p = pkcs7_pad(b'')
    assert p == b'\x10' * 16, p

    test = b'1234567890abc'
    p = pkcs7_pad(test)
    assert p == test + b'\3\3\3', p

    p = pkcs7_pad(test * 3)
    assert p == test * 3 + b'\x09' * 9, p

    p = pkcs7_unpad(test + b'\3\3\3')
    assert p == test, p

    p = pkcs7_unpad(test * 3 + b'\x09' * 9)
    assert p == test * 3, p

    try:                pkcs7_unpad(test)
    except ValueError:  pass
    else:               assert False, 'exception not raised'

    try:                pkcs7_unpad(b'x' + b'\x05' * 3)
    except ValueError:  pass
    else:               assert False, 'exception not raised'