[Tutor] Beginner's question: Looping through variable & list simultaneously

[Mark Lawrence]

On 03/12/2013 12:55, Rafael Knuth wrote:
> Hej there,
>
> I am writing a little throw away program in order to better understand
> how I can loop through a variable and a list at the same time. Here's
> what the program does and how it looks like: It counts the number of
> backpackers (assuming a growth rate of 15 % year on year) over the
> last five years:
>
> Backpackers = 1000000
> for x in range(2009, 2014):
>      Backpackers = Backpackers*1.15
>      print("In %d there were %d backpackers worldwide." % (x, Backpackers))
>
>>>>
> In 2009 there were 1150000 backpackers worldwide.
> In 2010 there were 1322500 backpackers worldwide.
> In 2011 there were 1520874 backpackers worldwide.
> In 2012 there were 1749006 backpackers worldwide.
> In 2013 there were 2011357 backpackers worldwide.
>
> Now I want to enhance that program a bit by adding the most popular
> country in each year. Here's what I want to get as the output:
>
>>>>
> In 2009 there were 1150000 backpackers worldwide and their most
> popular country was Brazil.
> In 2010 there were 1322500 backpackers worldwide and their most
> popular country was China.
> In 2011 there were 1520874 backpackers worldwide and their most
> popular country was France.
> In 2012 there were 1749006 backpackers worldwide and their most
> popular country was India.
> In 2013 there were 2011357 backpackers worldwide and their most
> popular country was Vietnam.
>
> I assume that I need to have a list like this:
>
> PopularCountries = ["Brazil", "China", "France", "India", "Vietnam"]
>
> But I struggle to modify the program above in a way that it loops
> properly through "Backpackers" and "PopularCountries".
>  From all my iterations there's only one that came at least halfway
> close to my desired result:
>
> PopularCountries = ["Brazil", "China", "France", "India", "Vietnam"]
> Backpackers = 1000000
> for x in range(2009, 2014):
>      Backpackers = Backpackers*1.15
>      PopularCountries = PopularCountries.pop()
>      print("In %d there were %d backpackers worldwide and their most
> popular country was %s." % (x, Backpackers, PopularCountries))
>
> It loops only once through "Backpackers" and "PopularCountries"
> (starting with the last item on the list though) and then it breaks:
>
>>>>
> In 2009 there were 1150000 backpackers worldwide and their most
> popular country was Vietnam.
> Traceback (most recent call last):
>    File "C:/Users/Rafael_Knuth/Desktop/Python/Backpackers.py", line 6,
> in <module>
>      PopularCountries = PopularCountries.pop()
> AttributeError: 'str' object has no attribute 'pop'
>
> My questions:
> Is there a way to use pop() to iterate through the list in a correct
> order (starting on the left side instead on the right)?
> If not: What alternative would you suggest?
> Do I need to rewrite the program in order to iterate through
> "Backpackers" and "PopularCountries" at the same time? (for example
> using a while instead of a for loop?)
> Or is there a way to modify my existing program?
> Should "PopularCountries" be a list or do I need a dictionary here?
>
> I am using Python 3.3.0.
>
> Thank you in advance!
>
> All the best,
>
> Rafael
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Loop around your list using the enumerate builtin function and an 
appropriate value for start, see 
http://docs.python.org/3/library/functions.html#enumerate

-- 
My fellow Pythonistas, ask not what our language can do for you, ask 
what you can do for our language.

Mark Lawrence