Data commit

Task/Playfair-cipher/Python/playfair-cipher.py

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+from string import ascii_uppercase
+from itertools import product
+from re import findall
+
+def uniq(seq):
+    seen = {}
+    return [seen.setdefault(x, x) for x in seq if x not in seen]
+
+def partition(seq, n):
+    return [seq[i : i + n] for i in xrange(0, len(seq), n)]
+
+
+"""Instantiate a specific encoder/decoder."""
+def playfair(key, from_ = 'J', to = None):
+    if to is None:
+        to = 'I' if from_ == 'J' else ''
+
+    def canonicalize(s):
+        return filter(str.isupper, s.upper()).replace(from_, to)
+
+    # Build 5x5 matrix.
+    m = partition(uniq(canonicalize(key + ascii_uppercase)), 5)
+
+    # Pregenerate all forward translations.
+    enc = {}
+
+    # Map pairs in same row.
+    for row in m:
+        for i, j in product(xrange(5), repeat=2):
+            if i != j:
+                enc[row[i] + row[j]] = row[(i + 1) % 5] + row[(j + 1) % 5]
+
+    # Map pairs in same column.
+    for c in zip(*m):
+        for i, j in product(xrange(5), repeat=2):
+            if i != j:
+                enc[c[i] + c[j]] = c[(i + 1) % 5] + c[(j + 1) % 5]
+
+    # Map pairs with cross-connections.
+    for i1, j1, i2, j2 in product(xrange(5), repeat=4):
+        if i1 != i2 and j1 != j2:
+            enc[m[i1][j1] + m[i2][j2]] = m[i1][j2] + m[i2][j1]
+
+    # Generate reverse translations.
+    dec = dict((v, k) for k, v in enc.iteritems())
+
+    def sub_enc(txt):
+        lst = findall(r"(.)(?:(?!\1)(.))?", canonicalize(txt))
+        return " ".join(enc[a + (b if b else 'X')] for a, b in lst)
+
+    def sub_dec(encoded):
+        return " ".join(dec[p] for p in partition(canonicalize(encoded), 2))
+
+    return sub_enc, sub_dec
+
+
+(encode, decode) = playfair("Playfair example")
+orig = "Hide the gold in...the TREESTUMP!!!"
+print "Original:", orig
+enc = encode(orig)
+print "Encoded:", enc
+print "Decoded:", decode(enc)