If statement not firing

Question

This code does a recursive bisection search for a character in a string.

When the print statements are not commented out, it seems to work well with the recursion and bisection, but the if statement that returns True does not seem to fire.

def isIn(char, aStr):
    '''
    char: a single character
    aStr: an alphabetized string

    returns: True if char is in aStr; False otherwise
    '''
    b = sorted(aStr)
    c = len(aStr)
    # print("string b " + str(b))
    # print("c " + str(c))
    # print("element middle: " + str(b[round(c/2)]))
    #print("char: " + str(char))
    #print(str(char) == str(b[round(c/2)]))
    if ((str(char) == str(b[round(c/2)]))): # this if statement does not seem to fire
        return True
    elif (c == 1 and char != str(b[round(c/2)])) or (c == 0 and char != "") :
        return False
        #print("false")
    else:

        #if str(char) == str(b[round(c/2)]):
         #   return True
           # print("true")
        if char > b[round(c/2)]:
            isIn(char, b[round(c/2):c])

        elif char < b[round(c/2)]:
            isIn(char, b[0:round(c/2)])
        else:
            return False
            #print('fales')

By "does not fire", do you mean that the condition `str(char) == str(b[round(c/2)])` does not evaluate to `True`? If indentation is the issue, this question is a moot point. — Seth Difley, Sep 18 '16 at 14:38
A dupe? http://stackoverflow.com/questions/15210646/i-expect-true-but-get-none — Łukasz Rogalski, Sep 18 '16 at 15:03
Thank you. You are correct. I did not have return before calling the recursive function. I appreciate the feedback, and spent several hours troubleshooting. Thanks — Ryan Jarvis, Sep 18 '16 at 15:06

score 1 · Accepted Answer · answered Sep 18 '16 at 14:39

1

You need to return the result of each recursive call.

This is a very common mistake, for some reason.

answered Sep 18 '16 at 14:39

Daniel Roseman

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score 0 · Answer 2 · answered Sep 18 '16 at 14:57

0

You shouldn't be using round in whatever that calculation is, as then you are using a float instead of an int as the index to the string.
use int instead:

str(b[int(c/2)]))

answered Sep 18 '16 at 14:57

Rolf of Saxony

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score 0 · Answer 3 · answered Sep 18 '16 at 15:07

This code works, has return before the recursive function calls:

def isIn(char, aStr):
'''
char: a single character
aStr: an alphabetized string

returns: True if char is in aStr; False otherwise
'''
b = sorted(aStr)
c = len(aStr)
# print("string b " + str(b))
# print("c " + str(c))
# print("element middle: " + str(b[round(c/2)]))
#print("char: " + str(char))
#print(str(char) == str(b[round(c/2)]))
if ((str(char) == str(b[int(c/2)]))): # this if statement does not seem to fire
    return True
elif (c == 1 and char != str(b[round(c/2)])) or (c == 0 and char != "") :
    return False
    #print("false")
else:

    #if str(char) == str(b[round(c/2)]):
     #   return True
       # print("true")
    if char > b[round(c/2)]:
        return isIn(char, b[round(c/2):c])

    elif char < b[round(c/2)]:
        return isIn(char, b[0:round(c/2)])
    else:
        return False
        #print('fales')

You're going to have to change all of the `round` statements to `int`. It didn't occur to me, that you would only change the first one. And while you are editing please alter the last statement to `#print('fails')`. Just a mild annoyance. — Rolf of Saxony, Sep 18 '16 at 16:07

If statement not firing

3 Answers3