PEP 308: Alternative conditional operator forms
evan at 4-am.com
Wed Feb 12 18:32:05 CET 2003
Michele Simionato wrote:
> "Cannot" in the sense "such a confusion (for the reader, not for the grammar)
> cannot be allowed in Python which is intended to be a language easy to read".
Ah, you meant "ought not" or "should not". I disagree, more of which below.
> Besides, tuple are expressions, not statements, I have nothing
> against parens in expressions.
This is a bit circular, but OK.
> If there is a precedent in the topic of converting statement to
> expressions, how to stop people asking for other conversions?
Say "no"? This is a slippery slope argument, and you're not alone in
finding it persuasive, but I don't buy it. As far as I can recall, the
only sorts of statements that anyone has ever suggested embedding in an
expression (on c.l.py, anyway) are assignment and conditional. I would
be perfectly happy to allow:
if (x = f()):
...with required parens. I'm not about to start lobbying for it, though.
> Who is going to use "then" as a variable name ??
Few people, most likely; I meant that as a bit of fun, not a serious
> I think the harm of having a "then" keyword is much
> *much* smaller than the harm of having statement->expression
The harm of a new keyword is that some code becomes
forward-incompatible. The "harm" of a conditional expression that looks
like a conditional statement is ___? If you answer, please elaborate
beyond "it would be confusing" -- what exactly would be the consequences
of that confusion?
>>In the spirit of your first objection above, we also have:
>>C then print x else print y
> Nick Vargish already answered to that.
I think you both missed my point. I realize that this is clearly a
SyntaxError, I just don't see this as being much different as an
objection to "_ then _ else _" than when you raised it:
> (if C: print x
> else: print y)
> would be a syntax error!
Placing any statement in any form of conditional expression is a
SyntaxError. If a naive coder were tempted to try it based on the
similarity to the if-statement syntax, they would immediately be
informed by the compiler that they can't do that. Checking the docs
would (presumably) reveal the explanation to them.
Evan @ 4-am
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