On Fri, May 10, 2013 at 2:48 PM, Guido van Rossum <guido@python.org> wrote:

I just spent a few minutes staring at a bug caused by a missing comma
-- I got a mysterious argument count error because instead of foo('a',
'b') I had written foo('a' 'b').

I had a similar experience just few weeks ago. The bug was in a long list written like this:

['item11', 'item12', ..., 'item17',

'item21', 'item22', ..., 'item27'

...

'item91', 'item92', ..., 'item97']

Clearly the bug crept in when more items were added. (I try to keep redundant commas at the end of the list to avoid this, but not everyone likes this style.)

Would it be reasonable to start deprecating this and eventually remove
it from the language?

+1, but I would start by requiring () around concatenated strings.