Ian Kelly <ian.g.ke...@gmail.com>:
> On Wed, Apr 6, 2016 at 8:14 AM, Marko Rauhamaa <ma...@pacujo.net> wrote:
>> Now, if Python had an unlimited range() iterator/iterable, you could use
>> a "for" statement to emulate "while".
>
> You can already do this.
>
>>>> class While:
> ... def __init__(self, predicate):
> ... self._predicate = predicate
> ... self._exited = False
> ... def __iter__(self):
> ... return self
> ... def __next__(self):
> ... if self._exited or not self._predicate():
> ... self._exited = True
> ... raise StopIteration
> ...
>>>> i = 0
>>>> for _ in While(lambda: i < 10):
> ... print(i)
> ... i += 1
> ...
> 0
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
Impressive!
>> As it stands, Python without "while" could only compute
>> primitive-recursive functions. However, you only need "while" a
>> maximum of one time in your whole program to perform an arbitrary
>> computation.
>
> So this is wrong.
I stand corrected.
However, BartC's No-Buzzword Python doesn't have classes... If he
allowed for types.SimpleNamespace, we could have:
========================================================================
import types
def While(predicate):
def __iter__():
return thingy
def __next__():
if thingy._exited or not predicate():
thingy._exited = True
raise StopIteration
thingy = types.SimpleNamespace(
_exited=False, __iter__=__iter__, __next__=__next__)
return thingy
========================================================================
However, that results in:
TypeError: 'types.SimpleNamespace' object is not iterable
Where's my bug? Or is CPython buggy? Or is it the documentation:
The iterator objects themselves are required to support the
following two methods, which together form the iterator protocol:
iterator.__iter__()
[...]
iterator.__next__()
<URL: https://docs.python.org/3/library/stdtypes.html#typeiter>
Why is a SimpleNamespace object not an iterator even though it provides
__iter__ and __next__?
Marko
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