PEP 255: Simple Generators

[Paul Svensson]

"Andrew Dalke" <dalke at acm.org> writes:

>Carsten Geckeler:
>>So Test is called like a function and returns an instance.  But why make a
>>different syntax ("class") for defining it?  Just because it returns an
>>instance instead an integer or another object?  According to your
>>argument, "def" would be fine.
>
>There isn't quite enough information to distinguish between at
>least some class definitions and function definitions without the
>use of a keyword.  Consider
>
>>>> class SuperTest:.
>... pass.
>...
>>>> def Test(SuperTest):.
>...     def __init__(self, spam):.
>...         self.spam = spam.
>...     def __str__(self):.
>...         return str(self.spam)
>>>> t = Test("eggs")
>>>> str(t)
>'None'
>>>>
>
>Changing the 'def Test' to 'class Test' changes the
>entire meaning of the code.

Of course -- as would changing to 'gen Test'.

Consider an alternate universe, 
where "def" is used to define all of classes, functions, and generators.
It's easy to tell one from the other:
	Generators use "yield",
	functions use "return",
	classes use neither.

Obviously,
someone decided that in the case of def/class,
this was not a good idea.
How is def/gen different ?

Try writing a generator that always yields a fixed result;
in some cases an empty list.
Which of these would you like to explain to a newbie ?

---------------------------------------
def one():		gen two():
    yield 1		    yield 1
			    yield 2
---------------------------------------
def empty():		gen empty():
    if 0:	 	   pass
        yield
---------------------------------------
def empty():		def empty():
    return iter(())	    return ()
---------------------------------------


	/Paul