Error: maximum recursion depth exceeded in comparison

Question

I am trying to find a character in an alphabetized string... Here is the code

def isIn(char, aStr):

        middleChar = len(aStr)//2
        if char == aStr[middleChar]:
            return True
        elif char < aStr[middleChar]:
            LowerHalf = aStr[:middleChar]
            return isIn(char, LowerHalf)
        elif char > aStr[middleChar]:
            UpperHalf = aStr[middleChar:]
            return isIn(char, UpperHalf)
        else:
            return False

print(isIn('a', 'abc'))

It returns True. But When I put

print(isIn('d', 'abc'))

it returns this error: maximum recursion depth exceeded in comparison; instead of False.

I don't understand whats wrong. Please tell me where is the logical mistake I am doing.

R L W R L W · Accepted Answer · 2017-10-08T06:57:19

With d, The program splits the string from abc and picks out UpperHalf bc. Then it searches the new string bc. It then returns 'c' from 'bc' as expected. Since d > c, the program goes chooses that condition and once again returns the upper half of string 'c', which is c. Hence the recursion. To fix this, you need a separate way of handling length 1 strings.

Error: maximum recursion depth exceeded in comparison

2 Answers