[Python-Dev] conditional expressions - add parens?
jimjjewett at gmail.com
Tue Mar 7 16:19:06 CET 2006
On 3/7/06, Paul Moore <p.f.moore at gmail.com> wrote:
> The parentheses around genexps were (AFAICT)
> different - without them, the grammar was ambiguous,
> so some way of disambiguating was needed.
The out-of-order evaluation is a very large change,
because now we have a situation where normal
parsing completes an expression, but needs to avoid
evaluating it, just in case.
Currently, we can write:
>>> if False:
>>> print r
>>> print 6
Traceback (most recent call last):
File "<pyshell#14>", line 1, in -toplevel-
NameError: name 'r' is not defined
In the above example, r doesn't get evaluated because
the if ahead of it says to skip that branch. But with
conditional expressions, that flow control is changed
from *later* in the program.
I don't think we'll see the equivalent of Intercal Suck
Points anywhere but intentionally obfuscated code,
but I do expect to see:
>>> side_effect() if condition
In fact, I think the below examples are reasonable uses
that do a better job of expressing intent than the if
statement would. I just don't like the mental backtrack
they require, and would like some sort of advance
warning. Parentheses at least tell me "You're not done
yet; keep reading."
>>> ack(r,r) if r not in cache
>>> log(message) if error_flag
More information about the Python-Dev