[Tutor] trouble getting a list to update

[Danny Yoo]

On Thu, 6 Jan 2005, Vincent Wan wrote:

> On Jan 6, 2005, at 12:59 PM, Danny Yoo wrote:
> > Can you show us a snippet of the file output?  I'm not immediately
> > seeing anything particular with your debugging output statements:
>
> > Like the computer, I don't yet understand what the problem is.  *grin*
>
> > If you can point us at the output that looks weird to you, and tell us
> > what you expected to see instead and why, that will help us a lot to
> > better understand the situation.


Hi Vincent,


Ok, now I understand and see the bug.  write_list() contains the problem:

###
def write_list(list_to_write, file_name):
     "Writes elements of a list, seperated by spaces, to a file"
     for each in list_to_write:
         file_name.write(str(list_to_write[each]) + ' ')
     file_name.write('\n')
###



The bug is here:

         file_name.write(str(list_to_write[each]) + ' ')

Do you see why this is buggy?  'each' is not an index into list_to_write,
but is itself an element of list_to_write.



You probably meant to write:

         file_name.write(str(each) + ' ')


Your list was mutating just fine: the output function simply was obscuring
what was happening.


Best of wishes to you!