Recursive_bisection_letter_finder.py

def isIn(char, aStr):
    '''
    char: a single character
    aStr: an alphabetized string
    
    returns: True if char is in aStr; False otherwise
    '''
    # Your code here
    if aStr == "":
        return False
    elif len(aStr) == 1:
        return aStr == char
    else:
        midindex = len(aStr)/2
        midchar = aStr[midindex]
        if char == midchar:
            return True
        elif char > midchar:
            return isIn(char, aStr[midindex:])
        else:
            return isIn(char, aStr[:midindex])