[Python-Dev] A Hygienic Macro System in Python?

[Duncan Booth]

On 18 Mar 2002, Skip Montanaro <skip@pobox.com> wrote:

>  I think a "lock" keyword would be
> appropriate:
> 
>     lock somelock:
>         do stuff
> 
> The biggest problem I found with the try/finally lock idiom was that
> "do stuff" can tend to get long, so the vertical distance between
> lock.acquire() and lock.release() can be substantial.  a lock
> statement/clause/macro would remove the need to worry about that
> visual distance. 

This is one of the areas that I think Microsoft got right in C#. C# has a 
using statement:
   using (resource-acquisition) embedded-statement
where resource-acquisition is a local variable declaration or a expression 
that creates an object with an IDisposable interface.

The using statement effectively wraps a try..finally around the embedded 
statement, and the finally calls the Dispose method of the object created 
in the resource-acquisition part.

I guess a direct translation into Python would be:
  using assignment_stmt: suite
and:
  using expression: suite

Which would be roughly equivalent to:
  __usingvar__ = assignment_stmt (or expression)
  try: suite
  finally:
      if isinstance(__usingvar__, tuple):
          for item in __usingvar__: item.Destroy()
      else:
    	     __usingvar__.Destroy()

-- 
Duncan Booth                                             duncan@rcp.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?