I saw some nonsense in a comment.

ifenum_type=='flag':# check for powers of twoforiinrange(_high_bit(low)+1,_high_bit(high)):if2**inotinvalues:missing.append(2**i)elifenum_type=='enum':# check for powers of oneforiinrange(low+1,high):ifinotinvalues:missing.append(i)

The nonsense in this code, present in the class EnumCheck, is the comment about powers of 1. What is meant is rather "checking the identifiers are contiguous".
I suggest replacing the comment with something more suitable.