Method returning an Iterable Object
Is there a way to return an iterable object ? class twoTimes: def __init__(self, n): self.__n = n def getNext(): self.__n *= 2 return self.__n t = twoTimes(5) while (n in t.getNext()): # while (n in t): print (n) -- Anjanesh Lekshmnarayanan -- http://mail.python.org/mailman/listinfo/python-list
Re: Method returning an Iterable Object
Anjanesh Lekshminarayanan wrote: Is there a way to return an iterable object ? class twoTimes: def __init__(self, n): self.__n = n def getNext(): self.__n *= 2 return self.__n t = twoTimes(5) while (n in t.getNext()): # while (n in t): print (n) Sure: class EveryOther: def __init__(self, seq): self.seq = seq self.idx = 0 def next(self): self.idx += 1 if self.idx = len(self.seq): raise StopIteration value = self.seq[self.idx] self.idx += 1 return value def __iter__(self): return self print [x for x in EveryOther(range(10)) [1, 3, 5, 7, 9] regards Steve -- Steve Holden+1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Method returning an Iterable Object
On Mon, 26 Jan 2009 22:01:21 +0530 Anjanesh Lekshminarayanan m...@anjanesh.net wrote: Is there a way to return an iterable object ? class twoTimes: def __init__(self, n): self.__n = n def getNext(): self.__n *= 2 return self.__n Rename getNext() to next() and create another method named __iter__() that just returns self. TwoTimes is now an iterator. You can also replace the whole class with a function thusly: def two_times(n): for k in itertools.count(1): yield n * (2**k) This function is then called a generator (because it generates an iterator). You can now say infinitely_doubling_numbers = two_times(2) for number in in infinitely_doubling_numbers: print number to the same effect as the iterator version above. python.org seems uncooperative at the moment, but look up iterators or the iterator protocol and generators if it works for you. t = twoTimes(5) while (n in t.getNext()): # while (n in t): print (n) You are aware that this is an infinite loop, as is my example above BTW? (Probably just an example, but I ask just in case.) Also, could it be that you mean for n in t? regards /W -- My real email address is constructed by swapping the domain with the recipient (local part). -- http://mail.python.org/mailman/listinfo/python-list
Re: Method returning an Iterable Object
You can also replace the whole class with a function thusly: def two_times(n): for k in itertools.count(1): yield n * (2**k) This function is then called a generator (because it generates an iterator). You can now say infinitely_doubling_numbers = two_times(2) for number in in infinitely_doubling_numbers: print number Oh..this is new. Will checkup itertools. Thanks. t = twoTimes(5) while (n in t.getNext()): # while (n in t): print (n) You are aware that this is an infinite loop, as is my example above BTW? (Probably just an example, but I ask just in case.) I was aware this was an infinite loop - just didnt want to put more code for an example. -- http://mail.python.org/mailman/listinfo/python-list
Re: Method returning an Iterable Object
On Tue, 27 Jan 2009 00:05:53 +0530 Anjanesh Lekshminarayanan m...@anjanesh.net wrote: You can also replace the whole class with a function thusly: def two_times(n): for k in itertools.count(1): yield n * (2**k) This function is then called a generator (because it generates an iterator). You can now say infinitely_doubling_numbers = two_times(2) for number in in infinitely_doubling_numbers: print number Oh..this is new. Will checkup itertools. Thanks. OK, happy I could help. But my point was the yield statement (in case you didn't know about yield). regards /W -- My real email address is constructed by swapping the domain with the recipient (local part). -- http://mail.python.org/mailman/listinfo/python-list
Re: Method returning an Iterable Object
But how come a raise StopIteration in the next() method doesnt need to be caught ? It works without breaking. class twoTimes: max = 10**10 def __init__(self, n): self.__n = n def next(self): if self.__n self.max: raise StopIteration self.__n *= 2 return self.__n def __iter__(self): return self t = twoTimes(5) c = 0 print (t.next()) print (t.next()) for n in t: print n Anjanesh -- http://mail.python.org/mailman/listinfo/python-list
Re: Method returning an Iterable Object
On Tue, Jan 27, 2009 at 1:16 PM, Anjanesh Lekshminarayanan m...@anjanesh.net wrote: But how come a raise StopIteration in the next() method doesnt need to be caught ? It works without breaking. Because this exception is specially dealt with when iterating over an iterator. The raise StopIteration is what causes the iteration to stop. Consider: x = EveryOther(xrange(10)) x.next() 0 x.next() 2 x.next() 4 x.next() 6 x.next() 8 x.next() Traceback (most recent call last): File stdin, line 1, in module File foo.py, line 12, in next raise StopIteration StopIteration x = EveryOther(xrange(10)) list(x) [0, 2, 4, 6, 8] cheers James -- http://mail.python.org/mailman/listinfo/python-list
Re: Method returning an Iterable Object
Anjanesh Lekshminarayanan wrote: But how come a raise StopIteration in the next() method doesnt need to be caught ? It works without breaking. The for-loop looks for and catches StopIteration. It is an essential part of what defines a finite iterator. (Note, in 3.0, next is renamed __next__ in conformance with all other special methods. In 2.6, the rename is optional, I believe.) class twoTimes: max = 10**10 def __init__(self, n): self.__n = n There is no reason to mangle the attribute name. Max should be a parameter, and self.max = max added to the init. def next(self): if self.__n self.max: raise StopIteration self.__n *= 2 return self.__n Are you sure you do not want to return once the initial value of n passed to init? def __iter__(self): return self Once you understand the above, you can rewrite it as a generator function: def two_times(num, stop): while num stop: yield num num *=2 The two last lines can be switches if desired. t = twoTimes(5) c = 0 print (t.next()) print (t.next()) for n in t: print n print(list(two_times(5,687))) [5, 10, 20, 40, 80, 160, 320, 640] Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
