For review: PEP 308 - If-then-else expression

[Roman Suzi]

On Mon, 10 Feb 2003, Andrew Koenig wrote:

>Erik> Well, it's unambiguous, but it could require some extra
>Erik> lookahead.  I'm no Python parser expert, but it seems to me the
>Erik> only case this happens is when the conditional expression is
>Erik> used as a standalone statement, e.g.
>
>Erik> 	if debug: sys.stderr.write('got here\n') else: None
>
>Why is extra lookahead required here?  The "if" is the first token in
>the statement, so it can only denote an if-statement, not an
>if-expression.  

In Python, expression is a standalone statement. So in case of 

if expr1: expr2 else: expr3

the parser will notice the difference only at "else".

>Then we look at the grammar, which says that
>an if-statement in this case is
>
>        "if" expression ":" suite "else" ":" suite
>
>and we see that a suite must end in a newline.


Sincerely yours, Roman Suzi
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