[Python-ideas] Where-statement (Proposal for function expressions)

[MRAB]

Greg Ewing wrote:
> Jan Kaliszewski wrote:
> 
>> while foo(x) and bar() where:
>>     foo = SOMETHING
>>     def bar():
>>         SOMETHING ELSE
>> do:
>>     THE
>>     LOOP
>>     BODY
> 
> That's kind of clever, although it does require
> modifying the while-loop syntax, and if you're
> doing that, there's not a lot of gain over
> introducing a dedicated loop-and-a-half syntax.
> 
> Also, once we're allowed 'where' clauses on
> while statements, people are going to want them
> on other kinds of statements as well:
> 
>   if a == b where:
>     a = foo()
>     b = blarg()
>   then:
>     ...
> 
>   class Ham(Spam) where:
>     class Spam:
>       ...
>   is:
>     ...
> 
>   def f(x = default) where:
>     default = whatever
>   as:
>     ...
> 
>   try:
>     ...
>   except eels where:
>     eels = something_bad()
>   do:
>     ...
> 
> Where do we stop?
> 
>> while foo(x) and bar():
>>     where:
>>         foo = SOMETHING
>>         def bar():
>>             SOMETHING ELSE
>>     THE
>>     LOOP
>>     BODY
> 
> I think I liked the first version better. There's
> something jarring about the unindent half way
> through without any keyword to mark the boundary.
> Also the bare 'where' relating to the previous line
> suggests some weird grammatical gymnastics going
> on.
> 
"do" might be a sufficiently generic word to cover all the cases.

     while ... where:
         ...
     do:
         ...


     if a == b where:
         ...
     do:
         ...

etc.