def Lex(num,x,y,z=''):
 """num = string length, x and y = placeholder for some char, z = pattern list """
 list = []
 palindromes = []
 pals = []
 
 patterns = []
 
 c = "%0" + str(num) +"d"
 for i in range(0, 2 ** num):
     list.append(str(c % int(bin(i)[2:])))
 for i in range(0,len(list)):
     list[i] = list[i].replace("0",x).replace("1",y)
     print str("%02d" % int(i+1)) + '. ' + list[i]
     if (list[i]==list[i][::-1]):
         palindromes.append(i+1)
	 pals.append(list[i])
 
     if len(z)>0:
	for n in range(0, len(z)):
	   if list[i][n] == z[n]:
 	      patterns.append(list[i]) 
 
 if len(palindromes)>0:
    print "\nPalindromes: " + str(palindromes) + "\n----\n\n"
 return pals,patterns
 
def LexUpTo(l,op,x,y,z=''):
 """print lex of length range""" 
 output = []
 output2 = []
 if op == "<":
    for i in range(1, l):
       tmp = Lex(i,x,y,z)
       output += tmp[0]
       output2 += tmp[1]
 
 
 print "Sorted palindromes:\n" 
 print sorted(output)
 
 print "\n\nPatterns sorted by alpha, len:\n"
 print sorted(output2)
 print sorted(output2, key=len)
 
Lex(5,'x','y',['x'])

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