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Generator state/parameters

David Mertz, Ph.D. mertz at gnosis.cx
Fri Dec 12 02:52:32 EST 2003 
|mertz at gnosis.cx (David Mertz, Ph.D.) wrote:
|>   >>> def echo():
|>   ...     message = [None]
|>   ...     while message[0] != "EXIT":
|>   ...         yield message
|>   ...
|>   >>> for mess in echo():
|>   ...     if mess[0] is not None: print mess[0]
|>   ...     mess[0] = raw_input("Word: ")

michele.simionato at poste.it (Michele Simionato) wrote previously:
|A more verbose but arguably more elegant way would be to wrap the
|generator in a class. Let me repost some code I wrote some time ago.
|class MyIterator(Iterator):
|    def __gen__(self):
|        self.x=1
|        yield self.x # will be changed outside the class
|        yield self.x
|
|iterator=MyIterator()
|print iterator.next()
|iterator.x=5
|print iterator.next()

I don't disagree, of course, with Michele's class-based approach.  For
something fleshed out, his style lets you do a lot more with the
underlying class.

But there *is* something awfully elegant about the function-like
definition syntax of simple generators.  Doing what I do in the simple
example--yielding a mutable object, and manipulating that object outside
the generator--feels very Pythonic to me.  I use a list for this, but a
different mutable object would work similarly (a dictionary, instance,
shelve, etc.)

But obviously, keep both styles in mind; either might be a good
solution to a problem.  It just depends on your needs and coding style.

Yours, David...

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