python - Output of testing if string is Palindrome -


output of testing if string palindrome

def ispalindrome1(s):     """assume s str        returns true if s palindrome;false otherwise.          punctuation marks, blanks, , capitalization          ignored."""     def tochars(s):         s = s.lower()# means:s = 'abcd',if s referenced s.lower,then s='abcd'.         ans = ''         c in s:             if c in'abcdefghijklmnopqrstuvwxyz':                 ans =ans+c         return ans      def ispal(s):         print ' ispal called with',s         if len(s)<=1:             print ' return true base case'             return true         else:             ans = s[0] == s[-1] , ispal(s[1:-1])             print ' return',ans,'for',s             return ans       return ispal(tochars(s))   def testispalindrome1():     print 'try doggod'     print ispalindrome1('doggod')     print 'try dogood'     print ispalindrome1('dogood')

execute function "testispalindrome1()" following result:

try doggod  ispal called doggod  ispal called oggo  ispal called gg  ispal called   **about return true base case  return true gg  return true oggo  return true doggod** true try dogood  ispal called dogood  ispal called ogoo  ispal called go  return false go  return false ogoo  return false dogood false

what's logic of execution on section in stars?

everytime recursion returned from, must continue method called. 

ans = s[0] == s[-1] , ispal(s[1:-1])  # branches off, other function call  print ' return',ans,'for',s  # waits recursion finish

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