[Python-Dev] Simple Switch statement

[Georg Brandl]

Raymond Hettinger wrote:
>>>No thanks.  That is its own can of worms.  The obvious solutions (like const
>>>declarations, macros, or a syntax to force compile-time expression 
>>>evaluation)
>>>are unlikely to sit well because they run afoul Python's deeply ingrained
>>>dynamism.
>>>    
>>>
>>
>>I think perhaps you haven't been paying close attention to Fredrik's 
>>proposal.
>>
> Yes, I have been.  That is one of the three options I listed above.  
> Each has its own issues.
> 
> The static() keyword works like Forth's brackets for forcing 
> compile-time evaluation.  The issue for us is that unlike other Python 
> expressions, there are inconvenient limitiations on what can be 
> expressed inside:
> 
>    five = 5
>    eight = [8]
>    def f(x, six=6):
>           seven =  7
>           a = static(five + 4)    # this is legal
>           b = static(six + 4)      # this is illegal
>           c = static(seven + 4) # this is illegal
>           d = static(eight + [4]) # this is illegal

Why would the last line be illegal?

> 
> That will be a perpetual maintenance trap and conundrum for newbies.

In contrary to other "newbie traps" such as mutable default arguments, if
this would give a clear exception message like
"function-local name cannot be used in static expression", I can't imagine
it would be a bigger problem than e.g. "why is my floating point result
incorrect".

Georg