crypto.cipher des cbc failure

>>> from Crypto.Cipher import DES
>>> DES.new('abcdefghijklmnop', DES.MODE_CBC, '1234567890123456')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/Crypto/Cipher/DES.py", line 108, in new
    return DESCipher(key, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/Crypto/Cipher/DES.py", line 63, in __init__
    blockalgo.BlockAlgo.__init__(self, _DES, key, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/Crypto/Cipher/blockalgo.py", line 401, in __init__
    self._cipher = factory.new(key, *args, **kwargs)
ValueError: Invalid key size (must be either 16 or 24 bytes long)

this should not be happened ?