searching starting index of sub-string in string

KMP.py

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+'''AUTHOR: Prashant kumar
+Python3 Concept: Knuth-Morris-Pratt (KMP) String Matching Algorithm
+GITHUB: https://github.com/Prashant0kgp
+
+Add your python3 concept below'''
+
+# Python program for KMP Algorithm
+def KMPSearch(word, txt):
+	A = len(word)
+	B = len(txt)
+
+	# create lst[] that will hold the longest prefix suffix
+	# values for pattern
+	lst = [0]*A
+	j = 0 # index for word[]
+
+	# Preprocess the pattern (calculate lst[] array)
+	computeLSTArray(word, A, lst)
+
+	i = 0 # index for txt[]
+	while i < B:
+		if word[j] == txt[i]:
+			i += 1
+			j += 1
+
+		if j == A:
+			print ("STARTING INDEX " + str(i-j))
+			j = lst[j-1]
+
+		# mismatch after j matches
+		elif i < B and word[j] != txt[i]:
+			# Do not match lst[0..lst[j-1]] characters,
+			# they will match anyway
+			if j != 0:
+				j = lst[j-1]
+			else:
+				i += 1
+
+def computeLSTArray(word, M, lst):
+	len = 0 # length of the previous longest prefix suffix
+
+	lst[0] # lst[0] is always 0
+	i = 1
+
+	# the loop calculates lst[i] for i = 1 to M-1
+	while i < M:
+		if word[i]== word[len]:
+			len += 1
+			lst[i] = len
+			i += 1
+		else:
+			# This is tricky. Consider the example.
+			# AAACAAAA and i = 7. The idea is similar
+			# to search step.
+			if len != 0:
+				len = lst[len-1]
+
+				# Also, note that we do not increment i here
+			else:
+				lst[i] = 0
+				i += 1
+# driver code
+txt = "ABDABACDABABCABAB"
+word = "ABABCABAB"
+KMPSearch(word, txt)