Recursive function in Python coming up with: "TypeError: 'int' object is not iterable"

Question

This function, that I got from this question, is as follows:

def f(n, p, k, t):
    return sum(sum(1 if n == 3 else
                   (0 if k == 1 else
                    (1/36) * f(n-1, p, k-1, t-(max(p,i)))
                    for i in xrange(1, 7)))
                   for p in xrange(1, 7))

print sum(f(5,j,3,15) for j in xrange(1, 7))

When I run this, I get this long traceback error sequence ending in:

File "C:/Users/r/Documents/school/IB/Computer Science HL/Other Languages/Problem240/Problem240 - recursive2.py", line 6, in <genexpr>
for p in xrange(1, 7))
TypeError: 'int' object is not iterable

Can someone please tell me what's going on? What is wrong with my code and how would I fix it? Thank you!

There really is no reason to write this as one giant expression. Are you just looking for "what did I get wrong here?" or "How can I organize this in a way that's readable enough for me to debug myself?" — abarnert
– abarnert, Commented Feb 21, 2013 at 0:47

andrew cooke · Accepted Answer · 2013-02-21 01:02:36Z

2

i think you mean

def f(n, p, k, t):
    return sum(sum(1 if n == 3 else
                   (0 if k == 1 else
                    (1/36) * f(n-1, p, k-1, t-(max(p,i)))) # <- more here
                   for i in range(1, 7)) # <- less here
               for p in range(1, 7))

print(sum(f(5,j,3,15) for j in range(1, 7)))

(i'm using python 3, but it's basically the same).

you have some parens wrong so the inner sum isn't a generator expression like you expect.

also see gnibbler's point below since you're using python 2

edited Feb 21, 2013 at 1:02

answered Feb 21, 2013 at 0:48

andrew cooke

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2 Comments

Ethan Brouwer Over a year ago

Thank you. I knew it was the problem with the parentheses. I just put the extra one in the wrong place. :D

John La Rooy Over a year ago

(1.0/36) for Python2 to force float division

John La Rooy · Accepted Answer · 2013-02-21 01:08:28Z

1

If you can't understand your own code, break it down into smaller parts

def f(n, p, k, t):
    ternary = (1 if n == 3 else 0 if k == 1 else 
        f(n-1, p, k-1, t-max(p,i))/36.0 for i in range(1, 7))

    inner_sum = sum(ternary)
    return sum(inner_sum for p in range(1, 7))

edited Feb 21, 2013 at 1:08

answered Feb 21, 2013 at 0:57

John La Rooy

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