It might be useful to introduce a new map() and filter() methods to iterators and iterables. Both methods should accept lambda/function which transforms a single argument into value. Both methods should return another iterator. # proposed methods usage: range(10).map(abs).filter(lambda x: x % 5 == 0) # existing equivalent: filter(lambda x: x % 5 == 0, map(abs, range(-10, 10))) # result: [10, 5, 0, 5] Rough equivalent of implementation: class iterator: def map(self, fn): for v in self: yield fn(v) def filter(self, fn): for v in self: if fn(v): yield v else: continue Introduction of such methods will allow to transform collections lazy without significant memory consumption (as was mentioned in http://bugs.python.org/issue912738).
I think this is quite a major change to Python and this needs a PEP BTW and therefore this bug no longer applies to Python 3. In Python 3 map returns an iterator. Even if you wanted to implement this feature in Python 2, it is not possible because in Python 2.7 (the only Python 2 release which is not in bug-fix mode) only minor enhancements are allowed. -1 for this proposal
Your proposal seems two-fold: (a) make map/filter lazy and (b) have them as methods instead of functions. It seems Tim borrowed Guido's time machine and already implemented (a) in Python 3.x, see http://docs.python.org/py3k/library/functions.html#map and http://docs.python.org/py3k/library/functions.html#filter. Your second proposal-- which is better suited for python-ideas, really --is obstructed by iterators being merely a protocol (the next/__next__ method) which makes it hard to add those methods to one particular type. (This very discussion pops up every so often for str.join too.) I'd recommend closing this issue.
As Robert noted, the map() and filter() builtins in Python 3 are already lazy and there's no reason to expand the iterator protocol for this functionality. Map and filter also have dedicated syntax in the form of comprehensions and generator expressions: itr = (x for x in map(abs, range(10)) if x % 5 == 0) Furthermore, the standard library already provides an entire module of tools for creating and working with lazy iterators in both Python 2 and Python 3: http://docs.python.org/library/itertools
History
Date
User
Action
Args
2022-04-11 14:57:31
admin
set
github: 59166
2012-05-30 11:01:16
ncoghlan
set
status: open -> closednosy: + ncoghlanmessages: + resolution: rejected
