calculate key length

vignere.py

@@ -1,5 +1,11 @@
 #!/usr/bin/python3
-import sys, getopt, os
+import sys, getopt, os, collections, math
+
+def chartonum(char):
+    return ord(char)-97
+
+def numtochar(int):
+    return chr(int+97)
 
 def encrypt(string,key):
     lowerstr=string.lower()
@@ -9,10 +15,10 @@ def encrypt(string,key):
     resultnums = []
     resultstring = ""
     for c in lowerstr:
-        strnums.append(ord(c)-97)
+        strnums.append(chartonum(c))
     print(strnums)
     for c in key:
-        keynums.append(ord(c)-97)
+        keynums.append(chartonum(c))
     print(keynums)
     keypointer=0
     for n in strnums:
@@ -20,7 +26,7 @@ def encrypt(string,key):
         keypointer = (keypointer+1) % (len(key))
     print(resultnums)
     for c in resultnums:
-        resultstring = resultstring+chr(c+97)
+        resultstring = resultstring+numtochar(c)
     print(resultstring)
 
 def decrypt(string,key):
@@ -31,18 +37,18 @@ def decrypt(string,key):
     resultnums = []
     resultstring = ""
     for c in lowerstr:
-        strnums.append(ord(c)-97)
-    print(strnums)
+        strnums.append(chartonum(c))
+    #print(strnums)
     for c in key:
-        keynums.append(ord(c)-97)
-    print(keynums)
+        keynums.append(chartonum(c))
+    #print(keynums)
     keypointer=0
     for n in strnums:
         resultnums.append((n-keynums[keypointer])%26)
         keypointer = (keypointer+1) % (len(key))
-    print(resultnums)
+    #print(resultnums)
     for c in resultnums:
-        resultstring = resultstring+chr(c+97)
+        resultstring = resultstring+numtochar(c)
     print(resultstring)
 
 def trigraphcount(string):
@@ -55,22 +61,26 @@ def trigraphcount(string):
             if index == -1:
                 break
             print(trigraph+' found at', index)
-            if not trigraph in distances and index!=i:
-                distances[trigraph] = index - i
+            offset = index - i
+            if not trigraph in distances and offset>0:
+                distances[trigraph] = [offset]
+            elif offset>0:
+                distances[trigraph].append(offset)
             index += 3
     #print(distances)
-    print(sorted(distances.items(), key=lambda x: x[1]))
+    #print(list(distances.values()))
+    dists = [item for sublist in list(distances.values()) for item in sublist]
+    #print(dists)
+    count = collections.Counter(dists)
+    most_commons = count.most_common(n=2)
+    print(most_commons)
+    key_len = math.gcd(most_commons[0][0], most_commons[1][0])
+    print(key_len)
+    lettercount(string,key_len)
+    #print(sorted(distances.items(), key=lambda x: x[1]))
 
 def lettercount(string,dist):
-    letters = {}
-    for i in range(0,len(string)-dist,dist):
-        print(string[i:i+dist])
-        for c in string:
-            if c in letters:
-                letters[c] = letters[c]+1
-            else:
-                letters[c] = 1
-    print(letters)
+    pass
 
 def main(argv):
     key = ""