[Tutor] Function for converting ints from base10 to base2?

[Jerry Hill]

On 2/21/07, Dick Moores <rdm at rcblue.com> wrote:
> But there's syntax(?) there I've never seen before. "['','-'][n<0]".
> I see it works:
>
>  >>> n = -6
>  >>> ['','-'][n<0]
> '-'
>  >>> n = 98
>  >>> ['','-'][n<0]
> ''
>
> What's this called? I'd like to look it up.

['', '-'] is a list with two elements: an empty string, and the string '-'.
[n<0] is an index into the list.

For example:
>>> a = ['First Element', 'Second Element']
>>> a[False]
'First Element'
>>> a[True]
'Second Element'

This works because int(True) is 1 and int(False) is 0.  Personally, I
find using boolean values to index a list to be hard to read.  If I
ever came back to looking at the code again, I'd rather have written
something like this:

sign = ''
if (n < 0): sign = '-'

It's an extra line of code, but it's a lot less cryptic to me.

--
Jerry