Seven undefined names: Missing imports?

[cclauss]

flake8 testing of https://github.com/pschmitt/pykeepass on Python 3.7.1

$ flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics

./pykeepass/attachment.py:46:19: F821 undefined name 'AttachmentError'
            raise AttachmentError('No such attachment id')
                  ^
./pykeepass/kdbx_parsing/twofish.py:74:26: F821 undefined name 'ECB'
            self.chain = ECB(self.cipher, self.blocksize)
                         ^
./pykeepass/kdbx_parsing/twofish.py:87:26: F821 undefined name 'CFB'
            self.chain = CFB(self.cipher, self.blocksize,self.IV,segment_size)
                         ^
./pykeepass/kdbx_parsing/twofish.py:91:26: F821 undefined name 'OFB'
            self.chain = OFB(self.cipher, self.blocksize,self.IV)
                         ^
./pykeepass/kdbx_parsing/twofish.py:95:26: F821 undefined name 'CTR'
            self.chain = CTR(self.cipher,self.blocksize,counter)
                         ^
./pykeepass/kdbx_parsing/twofish.py:106:26: F821 undefined name 'XTS'
            self.chain = XTS(self.cipher, self.cipher2)
                         ^
./pykeepass/kdbx_parsing/twofish.py:110:26: F821 undefined name 'CMAC'
            self.chain = CMAC(self.cipher,self.blocksize,self.IV)
                         ^
7     F821 undefined name 'AttachmentError'
7

[Evidlo]

First one was addressed already. As for the others, CBC is the only mode we use. Also I plan to get rid of twofish.py as soon as twofish support is added to pycryptodome.