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comparison Doc/tutorial/classes.rst @ 79691:05c8928362ee

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Merge __next__ method link fixes with 3.3.
author Ezio Melotti <ezio.melotti@gmail.com>
date Fri, 12 Oct 2012 13:46:37 +0300
parents 0cddf0bd19f8
children 65a3ba21c679
comparison
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79688:3534acfa8e37 79691:05c8928362ee
735 print(line) 735 print(line)
736 736
737 This style of access is clear, concise, and convenient. The use of iterators 737 This style of access is clear, concise, and convenient. The use of iterators
738 pervades and unifies Python. Behind the scenes, the :keyword:`for` statement 738 pervades and unifies Python. Behind the scenes, the :keyword:`for` statement
739 calls :func:`iter` on the container object. The function returns an iterator 739 calls :func:`iter` on the container object. The function returns an iterator
740 object that defines the method :meth:`__next__` which accesses elements in the 740 object that defines the method :meth:`~iterator.__next__` which accesses
741 container one at a time. When there are no more elements, :meth:`__next__` 741 elements in the container one at a time. When there are no more elements,
742 raises a :exc:`StopIteration` exception which tells the :keyword:`for` loop to 742 :meth:`__next__` raises a :exc:`StopIteration` exception which tells the
743 terminate. You can call the :meth:`__next__` method using the :func:`next` 743 :keyword:`for` loop to terminate. You can call the :meth:`__next__` method
744 built-in function; this example shows how it all works:: 744 using the :func:`next` built-in function; this example shows how it all works::
745 745
746 >>> s = 'abc' 746 >>> s = 'abc'
747 >>> it = iter(s) 747 >>> it = iter(s)
748 >>> it 748 >>> it
749 <iterator object at 0x00A1DB50> 749 <iterator object at 0x00A1DB50>
759 next(it) 759 next(it)
760 StopIteration 760 StopIteration
761 761
762 Having seen the mechanics behind the iterator protocol, it is easy to add 762 Having seen the mechanics behind the iterator protocol, it is easy to add
763 iterator behavior to your classes. Define an :meth:`__iter__` method which 763 iterator behavior to your classes. Define an :meth:`__iter__` method which
764 returns an object with a :meth:`__next__` method. If the class defines 764 returns an object with a :meth:`~iterator.__next__` method. If the class
765 :meth:`__next__`, then :meth:`__iter__` can just return ``self``:: 765 defines :meth:`__next__`, then :meth:`__iter__` can just return ``self``::
766 766
767 class Reverse: 767 class Reverse:
768 """Iterator for looping over a sequence backwards.""" 768 """Iterator for looping over a sequence backwards."""
769 def __init__(self, data): 769 def __init__(self, data):
770 self.data = data 770 self.data = data
817 o 817 o
818 g 818 g
819 819
820 Anything that can be done with generators can also be done with class based 820 Anything that can be done with generators can also be done with class based
821 iterators as described in the previous section. What makes generators so 821 iterators as described in the previous section. What makes generators so
822 compact is that the :meth:`__iter__` and :meth:`__next__` methods are created 822 compact is that the :meth:`__iter__` and :meth:`~generator.__next__` methods
823 automatically. 823 are created automatically.
824 824
825 Another key feature is that the local variables and execution state are 825 Another key feature is that the local variables and execution state are
826 automatically saved between calls. This made the function easier to write and 826 automatically saved between calls. This made the function easier to write and
827 much more clear than an approach using instance variables like ``self.index`` 827 much more clear than an approach using instance variables like ``self.index``
828 and ``self.data``. 828 and ``self.data``.