[Tutor] self keyword in recursive function

[Alan Gauld]

On 30/05/14 14:14, Ritwik Raghav wrote:
> I joined the topcoder community tomorrow and tried solving the
> PersistentNumber problem:

Time travel! I love it already... :-)

> 8*1 = 8. Thus, the persistence of 99 is 2. You will be given n, and you
> must return its persistence."
>
> It asks to define a function def getPersistence(self, n). I solved the
> problem in IDLE. My code is:

You seem to have solved the problem.
Your code could be cleaned up a little but it seems
to work. The fact that the exercise asks for a self
argument suggests that it is supposed to be part of
a class definition.

Is there a class definition anywhere that you are
supposed to extend?

|Some comments on the code below:

> def getPersistence(n,count = 0)

Since you never get passed count as an argument you
could just make it a variable. You only need it as
an argument if you use recursion but the problem
didn't ask for that...

>      product = 1
>      if len(str(n)) == 1:
>          return count
>      else:
>          a = str(n)
>          for i in range(len(a)):
>              product *= int(a[i])

This is not good Python style.
Its better to use

for c in a:
    product += int(c)

>          count += 1
>          return getPersistence(product,count)

Rather than using recursion you could have used
a while loop (untested code!):

if n < 10:
    return 0
product = 1
while True:
    count += 1
    a = str(n)
    for c in a:
       product *= int(c)
    if product < 10:
       break
return count

> Now plz help me to convert the above code in specified format. Or help
> me understand how to recreate the function as specified.

You have created a function that does what is needed, it just doesn't 
have a self parameter. self is only used when the function is part of a 
class definition.

Without sight of the class that it should be part of we can't offer much 
more help.


-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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