On 2009-04-02 18:08, andrew cooke wrote:
grocery_stocker wrote:
in summary: iterator is bound to one instance of "it", while some_func()
returns a new instance each time it is called.
BUT
while what you are doing is interesting, it is not the same as Python's
iterators, which use "yield" from a function and don't require storing a
value in a class. look for "yield" in the python docs. this comment
may
be irrelevant; i am just worried you are confusing the above (which
apart
from the mistake about instances is perfectly ok) and python's iterators
(which use next(), yield, etc).
Okay, one last question for now
When I have the follow class
class it:
... def __init__(self):
... self.count = -1
... def next(self):
... self.count +=1
... if self.count< 4:
... return self.count
... else:
... raise StopIteraton
...
value = it()
How comes I can;t go over 'value' like in the following
for x in value:
... print x
...
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: iteration over non-sequence
But yet, I can do...
value.next()
0
value.next()
1
value.next()
2
value.next()
3
replace return with yield and it might work.
i have to go eat, but if it doesn't read the python docs on iterators -
for example http://docs.python.org/reference/expressions.html#index-1825
No, .next() needs to be a regular function that returns a value. What he needs
is an __iter__() method that returns self. Alternately, __iter__ could be a
generator, and you wouldn't implement a .next() at all.
In [1]: class it(object):
...: def __init__(self):
...: self.count = -1
...: def __iter__(self):
...: return self
...: def next(self):
...: self.count += 1
...: if self.count < 4:
...: return self.count
...: else:
...: raise StopIteration
...:
...:
In [2]: class it2(object):
...: def __init__(self):
...: self.count = -1
...: def __iter__(self):
...: self.count += 1
...: while self.count < 4:
...: yield self.count
...: self.count += 1
...:
...:
In [3]: list(it())
Out[3]: [0, 1, 2, 3]
In [4]: list(it2())
Out[4]: [0, 1, 2, 3]
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
--
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