On Mon, 14 Nov 2016 07:02 am, Antoon Pardon wrote:
>
> Some time ago I read a text or saw a video on iterators and one thing
> I remember from it, is that you should do something like the following
> when working with iterators, to avoid some pitt falls.
>
> def bar(iterator):
> if iter(iterator) is iterator:
> ...
>
> However I can't relocate it and can't remember the what and how anymore.
> Does anyone know what this is about?
Probably something like this:
def function(iterable):
if iter(iterable) is iterable:
print("iterable is already an iterator")
assert hasattr(iterable, '__next__') # 'next' in Python 2
else:
print("iterable is not an iterator")
print("it may be a list, dict, string, etc.")
`iter(thing) is thing` is an easy way to check whether thing is an iterator.
I'm surprised that the inspect module doesn't appear to have isiterable and
isiterator functions. Here's my first attempt at both:
def isiterable(obj):
"""Return True if obj is an iterable, and False otherwise.
Iterable objects can be iterated over, and they provide either
an __iter__ method or a __getitem__ method.
Iteration over an object tries calling the object's __iter__
method (if any), then repeatedly calls __next__ on the result
until a StopIteration exception is raised (the Iterator
Protocol). Otherwise, it tries calling __getitem__ with
arguments 0, 1, 2, 3 ... until an IndexError exception is
raised (the Sequence Protocol).
"""
T = type(obj)
return hasattr(T, '__iter__') or hasattr(T, '__getitem__')
def isiterator(obj):
"""Return True if obj is an iterator, and False otherwise.
Iterators can be iterated over, and they provide the following
methods:
- __iter__ which returns itself
- __next__
Iteration over an iterator repeatedly calls __next__ until a
StopIteration exception is raised.
"""
T = type(obj)
if hasattr(T, '__iter__') and hasattr(T, '__next__'):
return iter(obj) is obj
return False
--
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.
--
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