How can I count and display my recursive steps in Python?

Question

I am trying to count how many times my program goes through my recursive statement and gives me my result. This is the code:

def days(amt):
    day = 0
    new = (amt*.05) + amt - 10

    if amt == 0:
        return 0

    elif amt == '':
        return

    elif new >= 0 and new <= 1000:
        day += 1
        return days(new)

print("In {} days, you'll have {}".format(day,new))

So when you call the function days(100), it calculates that it takes 15 days to reach new amount which less than 0 or greater than 1000 (and then it stops bc it satisfies the second elif condition).

So I want my output to look like this In 15 days, you'll have -7.892....

My problem is no matter where I place the counter, it doesn't count.

Padraic Cunningham · Accepted Answer · 2016-06-06 00:06:30Z

3

To persist the count you need to either use some global variable or use a parameter to do the counting then return both the count and the amt:

def days(amt, day=1):
    new = (amt * .05) + amt - 10

    if amt == 0:
        return day, 0

    elif 0 <= new <= 1000:
        return days(new, day + 1)
    return  day, new

Which gives you:

In [2]: print("In {} days, you'll have {}".format(*days(100)))
In 15 days, you'll have -7.89281794114

You cannot set day = 0 anywhere in the function as every call is going to reset it to 0. I also removes elif amt == '' as I cannot see how a function that takes an int/float should ever equal to an empty string.

edited Jun 6, 2016 at 0:06

answered Jun 5, 2016 at 23:09

Padraic Cunningham

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4 Comments

adhamncheese Over a year ago

The day +=1 under the elif statement ends up doubling the number of days. So you can take that out and leave the day + 1 in the recursive call. Otherwise, perfect! Thanks!

adhamncheese Over a year ago

Make day = 1 in the function call.

Padraic Cunningham Over a year ago

Yep, forgot I had the +=

adhamncheese Over a year ago

Perfect! Thank you!

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