Query on hailstone sequence program in python

Question

Below is the program written for hailstone sequence.

count = 0

def hailstone(n):
    """Print the terms of the 'hailstone sequence' from n to 1."""
    assert n > 0
    print(n)
    if n > 1:
        if n % 2 == 0:
            hailstone(n / 2)
        else:
            hailstone((n * 3) + 1)
    count = count + 1
    return count

hailstone(10)

After debugging this program, I see that object referenced by count that is part of global frame is not getting incremented within the function object hailstone, as per the below observation:

Any reason, why count does not get incremented?

score 1 · Answer 1 · answered Feb 02 '15 at 10:19

1

The problem is that the incremented count is local to the function. The count defined in the first line of the code is in global scope

Either

Pass it as an argument, i.e. def hailstone(n,count) and call it as hailstone(10,count)
Make your count global, by having a line, global count at the starting of your function

answered Feb 02 '15 at 10:19

Bhargav Rao

50,140
28
121
140

why Cpython does not recognise that `count` is global? – overexchange Feb 02 '15 at 10:21
@overexchange It is because Py is dynamic scoped – Bhargav Rao Feb 02 '15 at 10:21
Dynamic scoped, what does that mean? – overexchange Feb 02 '15 at 10:22
@overexchange Read [this](http://stackoverflow.com/questions/291978/short-description-of-python-scoping-rules) You will understand it better. Hopefully it helps clear your doubt :) – Bhargav Rao Feb 02 '15 at 10:23

Query on hailstone sequence program in python

1 Answers1