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

Ian Bicking ianb at colorstudy.com
Sat Feb 8 04:10:38 CET 2003


On Fri, 2003-02-07 at 20:40, Andrew Dalke wrote:
> One other thing I came up with.  I'll often write
> 
> x = None
> if s.find("spam"):
>   x = "eggs?"
> 
> I do this because it guarantees that no matter what happens in the
> if statement, the 'x' will be initialized.  That's handy in more complicated
> if statements.  Also, it saves a line ;)
> 
> Take away the newlines and replace the ": x =" with "else"
> 
> x = None if s.find("spam") else "eggs?"
> 
> and the behaviour is exactly opposite.  I wonder how many
> times people will make that mistake?

I actually found this case to be a compelling argument for an if
expression.

  x = "eggs?" if s.find("spam") else None

Taht puts "eggs?" right out in front, which is good because "eggs?" is
the interesting and useful value for x, while None is just a sort of
default value.  So by switching the order I think the readability is
improved. This argument has made me think that the (true if cond else
false) form is better than (if cond then true else false) or (cond ?
true : false) form, even though initially I thought that order seemed
much more natural.  I credit this change in opinion to the maturity and
new experiences I've had since I initially thought about this, oh so
many hours ago.

-- 
Ian Bicking  ianb at colorstudy.com  http://colorstudy.com
4869 N. Talman Ave., Chicago, IL 60625  /  773-275-7241
"There is no flag large enough to cover the shame of 
 killing innocent people" -- Howard Zinn





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