Why is the interpreter is returning a 'reference'?

Zachary Ware zachary.ware+pylist at gmail.com
Mon Feb 17 18:14:10 CET 2014


On Mon, Feb 17, 2014 at 11:00 AM, Nir <nirchernia at gmail.com> wrote:
>>>> k = ['hi','boss']
>>>>
>>>> k
> ['hi', 'boss']
>>>> k= [s.upper for s in k]
>>>> k
> [<built-in method upper of str object at 0x00000000021B2AF8>, <built-in method upper of str object at 0x0000000002283F58>]
>
> Why doesn't the python interpreter just return
> ['HI, 'BOSS'] ?

It's just doing exactly what you are telling it to :).  Your list
comprehension is constructing a list consisting of the 'upper' method
(which are themselves objects, able to be passed around just like any
other value) for each string object in list 'k'.  Consider this:

   >>> k = ['hi', 'boss']
   >>> s = k[0]
   >>> s
   'hi'
   >>> s.upper  # this just accesses the 'upper' attribute of 's',
which turns out to be its 'upper' method
   <built-in method upper of str object at 0xdeadbeef>
   >>> s.upper() # this actually calls the 'upper' method on 's'
   'HI'

Change your comprehension to actually call the upper method like so:
"k = [s.upper() for s in k]".  It will do what you expected with that
change.

Hope this helps,

-- 
Zach



More information about the Python-list mailing list