Apparently you encrypt that specific string using DES. DES has a 56 bit key size and a 64 bit block size, so you use your 7 byte string as the key and the 8 byte string as the block, and it should work without any contradictions.

But it looks like pyDes requires an 8 byte key, and it really shouldn't. As far as I can tell, that's a bug and it breaks the algorithm - some of the code tries to do things in the 56-bit way with circular shifts (in __create_sub_keys), but it goes wrong because there's an extra 8 bits on the end of one of its lists. (By testing with some values, the output seems to depend on all but the last one bit of the 8-byte key, so it's not simply ignoring the 8th byte.)

So pyDes just seems broken - you should probably find a different implementation, or try to fix it yourself, and then find some reliable examples of DES encryption to compare it against to make sure it's giving the correct answers.