[Python-Dev] conditional expressions? (original) (raw)

Guido van Rossum guido@python.org
Mon, 15 Oct 2001 15:34:19 -0400

Well, the examples I saw looked like

x = (if (if e1 then e2 else e3) then e4 else e5) Seems to me that those inner parens are there to separate the inner conditional from the trailing parts of the outer conditional: x = ( if ( if ( ^ this is not there

e1 then e2 else e3 ) then e4 else e5 )

Whether or not that's what they are in a language parser sense, they sure look like it to the human eye.

They are syntactically unnecessary; they are mostly for guidance of the human reader. If I saw a piece of code that read

x = if if if x == 1 then y else z then p else q then a else b

I would get a strong urge to commit illegal violence against the author. If on the other hand I saw

x = if (if (if x == 1 then y else z) then p else q) then a else b

I might be willing to sit down and figure out what it meant -- maybe with the help of a parentheses-balancing command in my editor.

Tim> I'm not concerned about 21 bad arguments versus 20 .

That 21st argument will be a little stronger than the other, because it will go something like, "Why can't we have delimiters for block statements? After all, we have them in conditional expressions." The reference, instead of being to another language, will be to Python itself.

Sorry, I still don't get this at all. A conditional expression is still an expression. Curly brances are a statement-level concept. What am I missing? Where is the similarity between the use of { } and ( ) in C/Java/C++/Perl?

--Guido van Rossum (home page: http://www.python.org/~guido/)