  Python implementation of permutations is presented. Three classes are
introduced: Perm for permutations, Group for permutation groups, and PermError
to report any errors for both classes. The class Perm is based on Python
dictionaries and utilize cycle notation. The methods of calculation for the
perm order, parity, ranking and unranking are given. A random permutation
generation is also shown. The class Group is very simple and it is also based
on dictionaries. It is mainly the presentation of the permutation groups
interface with methods for the group order, subgroups (normalizer, centralizer,
center, stabilizer), orbits, and several tests. The corresponding Python code
is contained in the modules perms and groups.
