On 25/07/2020 06:35, Random832 wrote:
On Tue, Jul 21, 2020, at 15:54, Terry Reedy wrote:
The transformers should be once-through iterators because they can be
passed once-through interators. I suppose one could make them iterables
and add an attribute 'pristine' set to True in __init__ and False in
__iter__, but why have 2 objects instead of 1 when there is not gain in
function?
Why not just allow them to be iterated multiple times, and the underlying
iterator/iterable either handles that or doesn't as the case may be? We don't have a hard
API distinction between iterables and iterators, all iterators are "iterable"
in the sense that they have their own __iter__ method that returns self.
i.e. the equivalent of
class map:
def __init__(self, func, obj): ...
def __iter__(self): for x in iter(self.obj): yield self.func(x)
That way if it is passed a once-through iterator, it is a once-through iterator
with a couple extra steps, if passed an iterable it's an iterable.
If the design calls for a single iteration of the contents of some
container (for example), then need a signal to indicate 'end of data',
ie StopIteration.
Conversely, if prepared to iterate continuously, don't ever want to see
that exception.
How to differentiate?
Solution already available:
perhaps cycle() or chain()
itertools — Functions creating iterators for efficient looping
https://docs.python.org/3/library/itertools.html
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Regards =dn
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