# [Tutor] Range within a range

bob gailer bgailer at gmail.com
Fri Apr 11 21:30:23 CEST 2014

On 4/11/2014 1:13 PM, Andoni Gorostiza wrote:
> Hi tutor. I need your help with something I don't understand. In the
> tutorial, it mentions an example of a range within a range. I'll keep
> it simplified. How exactly does this work? I'll provide a few examples.
>
> >>> for x in range(0,5):
> ...for n in range(0,5):
> ...      print(x)
>
> >>> for x in range(0,5):
> ...for n in range(0,5)
> ...      print(n)
>
> This one comes from the tutorial:
>
> >>>for  n  in  range(2,  10):
> ...     for  x  in  range(2,  n):
> ...         if  n  %  x  ==  0:
> ...             print(n,  'equals',  x,  '*',  n//x)
> ...             break
> ...     else:
> ...         # loop fell through without finding a factor
> ...         print(n,  'is a prime number')
> ...
> 2 is a prime number
> 3 is a prime number
> 4 equals 2 * 2
> 5 is a prime number
> 6 equals 2 * 3
> 7 is a prime number
> 8 equals 2 * 4
> 9 equals 3 * 3
> Can you explain what is going on?
pencil and paper you play computer - "execute" (write) the code one step
at a time and write down what happens. Very simple example:
execute:                       change:
for x in range(0,2):      x == 0
for n in range(0,2):   n == 0
print(x)                     output == 0
next for n                   n == 1
print(x)                     output == 0
next for x                     x == 1
for n in range(0,2):   n == 0
print(x)                     output == 1
keep going - at each step write what executes and what changes or happens

When you run into an operation you don't understand stop and either
- look it up