[Python-ideas] breaking out of module execution

[Terry Reedy]

On 4/25/2012 4:27 PM, Ron Adam wrote:

> I was just trying to point out a module is closer to a class than it is
> to a function, and that is a good thing.

Each should only be executed once, and this is enforced for modules by 
the sys.modules cache.

 > Allowing a return or break in a
> module could make things more confusing.

Agreed.

It is not actually necessary for functions to have an explicit return 
statement. I believe that there are languages that define the function 
return value as the last value assigned to the function name.

def fact(n):
   if n > 1: fact = n*fact(n-1)
   else: fact = 1

(This is pretty close to how mathematicians might write the definition. 
It does, however, require special-casing the function name on the left 
of '='.)

'return' is, however, useful for returning out of more deeply nested 
constructs, especially loops, without setting flag variables or having 
multi-level breaks. This consideration does not really apply to the use 
case for module return.

A virtue of defining everything in Python and then trying to import the 
accelerated override is that different implementations and versions 
thereof can use the same file even though they accelerate different 
parts and amounts (even none) of the module.

-- 
Terry Jan Reedy