"""
Source code for math-teach post
by Kirby Urner / OST
(c) GNU Public License, 2011
"""
import string, random
charset = list(string.ascii_lowercase + " ")
def make_perm( ):
"make some random permutation object mapping " ",a-z into itself"
target = charset[:] # copy all
random.shuffle(target) # in place reordering
return Pobject(dict( zip(charset, target)))
class Pobject:
"""
permutation objects are instantiated with a dict. they
may be multiplied and/or inverted
"""
def __init__(self, perm):
self.perm = perm
def encrypt(self, plaintext):
e = ''
for char in plaintext:
e += self.perm[char]
return e
def decrypt(self, ciphertext):
e = ''
inv = ~self # invert the permutation
return inv.encrypt(ciphertext)
def __invert__(self):
invdict = {}
for char in self.perm:
invdict[self.perm[char]] = char
return Pobject(invdict)
def __mul__(self, other):
output = {}
for char in self.perm:
output[char] = other.perm[self.perm[char]]
return Pobject(output)
def __repr__(self, abbrev = False):
return str(sorted(self.perm.items(), key=lambda t: t[0]))
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