On Monday, December 7, 2015 at 8:14:46 PM UTC-5, Robin Koch wrote: > Am 08.12.2015 um 02:05 schrieb Robert: > > Hi, > > When I learn for loop with below link: > > > > http://www.shutupandship.com/2012/01/understanding-python-iterables-and.html > > > > it has such explanation: > > > > \\\\\\\\\ > > for loop under the hood > > > > First let's look at the for loop under the hood. When Python executes the > > for loop, it first invokes the __iter__() method of the container to get > > the > > iterator of the container. It then repeatedly calls the next() method > > (__next__() method in Python 3.x) of the iterator until the iterator > > raises a > > StopIteration exception. Once the exception is raised, the for loop ends. > > \\\\\\\\\ > > > > When I follow a list example from the above link, and one example of myself: > > > > ////////// > > xx=[1,2,3,4,5] > > > > xx.next > > --------------------------------------------------------------------------- > > AttributeError Traceback (most recent call last) > > <ipython-input-76-dd0716c641b1> in <module>() > > ----> 1 xx.next > > > > AttributeError: 'list' object has no attribute 'next' > > > > xx.__iter__ > > Out[77]: <method-wrapper '__iter__' of list object at 0x000000000A1ACE08> > > > > for c in xx: print c > > 1 > > 2 > > 3 > > 4 > > 5 > > ////////////// > > > > I am puzzled that the list examples have no next method, but it can run as > > a for loop. Could you explain it to me the difference? > > Lists don't have a next method. Their iterators have: > > xx.__iter__().__next__() > > or > > xxIterator = xx.__iter__() > xxIterator.__next__() > xxIterator.__next__() > xxIterator.__next__() > xxIterator.__next__() > xxIterator.__next__() > > That's also what your quoted paragraph states: > > | It then repeatedly calls the next() method > | (__next__() method in Python 3.x) of the iterator > > -- > Robin Koch
I use Python 2.7. I have tried these commands: xx=[1,2,3,4,5] xx.__iter__ Out[2]: <method-wrapper '__iter__' of list object at 0x000000000A1B85C8> xx.__iter__().__next__() --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-3-980bcf1bbf42> in <module>() ----> 1 xx.__iter__().__next__() AttributeError: 'listiterator' object has no attribute '__next__' xx.__iter__.__next__ --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-4-df8d8c6955e2> in <module>() ----> 1 xx.__iter__.__next__ AttributeError: 'method-wrapper' object has no attribute '__next__' xx.__iter__() Out[5]: <listiterator at 0xa211780> xx.__iter__().__next__ --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-6-92f21313d62e> in <module>() ----> 1 xx.__iter__().__next__ AttributeError: 'listiterator' object has no attribute '__next__' xxIterator = xx.__iter__() xxIterator Out[8]: <listiterator at 0xa2115c0> xxIterator.__next__() --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-9-5b74e35c2c6e> in <module>() ----> 1 xxIterator.__next__() AttributeError: 'listiterator' object has no attribute '__next__' for c in xx: print c 1 2 3 4 5 ------------ I don't find a way to show __next__ yet. Can we explicitly get the iterator for a list? Thanks, -- https://mail.python.org/mailman/listinfo/python-list
