On 3/7/2013 11:00 AM, Ian Kelly wrote:
But on this point, you are correct. The mongoengine QuerySet.__iter__
method is defined as:
def __iter__(self):
self.rewind()
return self
This is unfortunate design. Not only does it mean that the iterator's
__len__ method cannot be trusted (what should the __len__ of a
partially exhausted iterator return?), but it also means that requesting
an iterator over the QuerySet will also silently invalidate any
existing iterators.
I view that design as a violation of the iterator protocol and hence a
program bug. __iter__ should either *just* return self (if the self is
an iterator) or return a new object (if self is a non-iterator
iterable). File objects are iterators and .__iter__ does not rewind.
>>> f = open("f:/python/mypy/tem.py")
>>> next(f)
'class myit(list):\n'
>>> f2 = iter(f)
>>> f2 is f
True
>>> next(f2)
" def __bytes__(self): return b'hello'\n"
--
Terry Jan Reedy
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