simple linear time algorithm for finding longest palindome substring in a give string

subpalindrome.py

def longest_subpalindrome_slice(s):
  longest=(0,0)
	start_idx=0 #index of palindrone ending at i
	repeated = True
  #loop invariant we know longest palindrome in s[0:i]
  #and we know longest palidrom ending at i
	for i in xrange(1,len(s)):  
		if(start_idx != 0 and s[start_idx-1] == s[i]) :
			start_idx = start_idx-1
			repeated = False
		elif (not repeated or s[i] != s[i-1]):
			start_idx = i
			repeated = True
		longest = max(longest, (start_idx,i),key=lambda(l,r): r-l) 
	
	return (longest[0], longest[1]+1)
	
def test():
  
    L = longest_subpalindrome_slice
    assert L('racecar') == (0, 7)
    assert L('Racecar') == (0, 7)
    assert L('RacecarX') == (0, 7)
    assert L('Race carr') == (7, 9)
    assert L('') == (0, 0)
    assert L('something rac e car going') == (8,21)
    assert L('xxxxx') == (0, 5)
    assert L('Mad am I ma dam.') == (0, 15)
    assert L('hannnnah') == (0, 8)
    assert L('abcerehannnnah') == (6, 14)

    return 'tests pass'