Re: Need instruction on how to use isinstance
Hans Mulder wrote: > There's also: hasattr(, '__call__'). It works in both 2.x and 3.x. Good work, Hans. I do find that to be a more pythonic approach, personally, being more concerned with an object's ability than its abstract type. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
alex23 wrote: Stephen Hansen wrote: P.S. The removal of callable is something I don't understand in Python 3: while generally speaking I do really believe and use duck typing, I too have on occassion wanted to dispatch based on 'is callable? do x'. Sometimes its not convenient to do so via duck typing. Its rare. But it is there. That isinstance()/issubclass got a boost in power with the ABC's and registering, while at the same time the ability to introspect about the function-y callable-y ness of a function was removed? Makes no sense to me. But alas! There's always: isinstance(, collections.Callable) There's also: hasattr(, '__call__'). It works in both 2.x and 3.x. -- HansM -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On 6/27/10 10:09 PM, alex23 wrote: Stephen Hansen wrote: What the hell? When did that show up? o.O (Did I not pay attention enough during the ABC conversations? It seemed so boring). The PEPs& post-release docs detailing Py3 changes were worth reading, it's noted in the sections on changes to built-ins: http://www.python.org/dev/peps/pep-3100/ http://docs.python.org/py3k/whatsnew/3.0.html I've actually read nearly all of that multiple times-- I tend to idly re-read such things. But not everything sticks (as its usually late like now and I'm multitasking and just exploring curiously). Callable in collections (and the ABC's in collections-- I swear I thought they were in a module of their own) totally didn't sink in. A) how is Callable a collection, in any way shape or form? And B) does that really return True for everything callable-esque? (I don't have a 3.x to play with on this temporary computer) A) I was tempted to say "it's a collection of code" :) But really, the role of the collections model has expanded in 3.x to also provide a repository for ABCs: "In addition to containers, the collections module provides some ABCs (abstract base classes) that can be used to test whether a class provides a particular interface, for example, whether it is hashable or a mapping." http://docs.python.org/py3k/library/collections.html The documentation might say something crazy, but just because its *officially* crazy doesn't make it any less actually crazy. Just because most of the ABC's are vaguely collection-related, doesn't mean we should put them all into the collections module if there's some which aren't really collection-ish. It argues for either putting different ABC's in different places (say, Callable in functools? Who knows) or just putting them all in a single module. I dunno which: its far too late to do anything about now, but yeah. Re-defining a module to suddenly include various random tidbits which aren't even really related to that module's purpose counts as crazy in my book. I don't often think, "That's crazy." about Python, too. And although I'm not really in a place to use Python 3 yet, I do try to learn more and more of it as time goes on and play with it (and experiment with it) so that when I'm able, I'll be ready. And so far I've been largely very pleased, although Python 2 was rarely crazy (print >>crazy, "not withstanding") I've been pleased with the less odd edges as I explore Py3. Until now. Oh well, nothing can be perfect. :) -- ... Stephen Hansen ... Also: Ixokai ... Mail: me+list/python (AT) ixokai (DOT) io ... Blog: http://meh.ixokai.io/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On Sun, Jun 27, 2010 at 9:54 PM, Stephen Hansen wrote: > On 6/27/10 9:30 PM, alex23 wrote: >> Stephen Hansen wrote: >>> P.S. The removal of callable is something I don't understand in Python >>> 3: while generally speaking I do really believe and use duck typing, I >>> too have on occassion wanted to dispatch based on 'is callable? do x'. >>> Sometimes its not convenient to do so via duck typing. Its rare. But it >>> is there. That isinstance()/issubclass got a boost in power with the >>> ABC's and registering, while at the same time the ability to introspect >>> about the function-y callable-y ness of a function was removed? Makes no >>> sense to me. But alas! >> >> There's always: isinstance(, collections.Callable) > > What the hell? When did that show up? o.O (Did I not pay attention enough > during the ABC conversations? It seemed so boring). > > A) how is Callable a collection, in any way shape or form? Completely agree, see my prior reply. > And B) does that > really return True for everything callable-esque? (I don't have a 3.x to > play with on this temporary computer) You don't even need 3.x; it was added in 2.6. The new magic of __instancecheck__ makes it possible. See http://docs.python.org/reference/datamodel.html#customizing-instance-and-subclass-checks Cheers, Chris -- Very cool new magic, eh? http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
Stephen Hansen wrote: > What the hell? When did that show up? o.O (Did I not pay attention > enough during the ABC conversations? It seemed so boring). The PEPs & post-release docs detailing Py3 changes were worth reading, it's noted in the sections on changes to built-ins: http://www.python.org/dev/peps/pep-3100/ http://docs.python.org/py3k/whatsnew/3.0.html > A) how is Callable a collection, in any way shape or form? And B) does > that really return True for everything callable-esque? (I don't have a > 3.x to play with on this temporary computer) A) I was tempted to say "it's a collection of code" :) But really, the role of the collections model has expanded in 3.x to also provide a repository for ABCs: "In addition to containers, the collections module provides some ABCs (abstract base classes) that can be used to test whether a class provides a particular interface, for example, whether it is hashable or a mapping." http://docs.python.org/py3k/library/collections.html B) In a quick test in 3.1.2, it returned true for a function, a bound and unbound lambda, and an instance of a class with a __call__ defined. If there's any other kind of callable you can think of, let me know and I'll be happy to test it. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On 6/27/10 9:47 PM, Chris Rebert wrote: There's always: isinstance(, collections.Callable) Why in Guido's name is that in the collections module of all places? What hath callability to do with container objects? What he said! Minus the blasphemy. It's Benevolent _Dictator_ For Life. Not Benevolent _Diety_ For Life. Just because a man has an uncanny sense of style (in the programming sense) and a time machine, doesn't a god make. -- ... Stephen Hansen ... Also: Ixokai ... Mail: me+list/python (AT) ixokai (DOT) io ... Blog: http://meh.ixokai.io/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On 6/27/10 9:30 PM, alex23 wrote: Stephen Hansen wrote: P.S. The removal of callable is something I don't understand in Python 3: while generally speaking I do really believe and use duck typing, I too have on occassion wanted to dispatch based on 'is callable? do x'. Sometimes its not convenient to do so via duck typing. Its rare. But it is there. That isinstance()/issubclass got a boost in power with the ABC's and registering, while at the same time the ability to introspect about the function-y callable-y ness of a function was removed? Makes no sense to me. But alas! There's always: isinstance(, collections.Callable) What the hell? When did that show up? o.O (Did I not pay attention enough during the ABC conversations? It seemed so boring). A) how is Callable a collection, in any way shape or form? And B) does that really return True for everything callable-esque? (I don't have a 3.x to play with on this temporary computer) -- ... Stephen Hansen ... Also: Ixokai ... Mail: me+list/python (AT) ixokai (DOT) io ... Blog: http://meh.ixokai.io/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On Sun, Jun 27, 2010 at 9:30 PM, alex23 wrote: > Stephen Hansen wrote: >> P.S. The removal of callable is something I don't understand in Python >> 3: while generally speaking I do really believe and use duck typing, I >> too have on occassion wanted to dispatch based on 'is callable? do x'. >> Sometimes its not convenient to do so via duck typing. Its rare. But it >> is there. That isinstance()/issubclass got a boost in power with the >> ABC's and registering, while at the same time the ability to introspect >> about the function-y callable-y ness of a function was removed? Makes no >> sense to me. But alas! > > There's always: isinstance(, collections.Callable) Why in Guido's name is that in the collections module of all places? What hath callability to do with container objects? Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
Stephen Hansen wrote: > P.S. The removal of callable is something I don't understand in Python > 3: while generally speaking I do really believe and use duck typing, I > too have on occassion wanted to dispatch based on 'is callable? do x'. > Sometimes its not convenient to do so via duck typing. Its rare. But it > is there. That isinstance()/issubclass got a boost in power with the > ABC's and registering, while at the same time the ability to introspect > about the function-y callable-y ness of a function was removed? Makes no > sense to me. But alas! There's always: isinstance(, collections.Callable) -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On 6/27/10 8:04 PM, Steven W. Orr wrote: On 6/27/2010 10:25 PM, Stephen Hansen wrote: On 6/27/10 7:09 PM, Steven W. Orr wrote: So, my question is, what value can I use as the 2nd arg to isinstance to see if foo is a function? And while I'm on the subject, what types does isinstance not support? Does it have to be a function? -- There's quite a few things which are function-y enough that you really should accept them even if they may not be technically a /function/. Like a class instance with the __call__ method defined wrapping a function as a decorator. Or a bound method, really. In Python 2.x, you can use callable(fun) -- that goes away in Py3 though. But personally, I think this is the wrong approach. Ok, you just asked great questions, and your questions were based on what I didn't tell you. I'm trying to teach myself about how __metaclass__ can be used as a substitute for LSD. ;-) [snip] Ah. In that case, bearing in mind this won't work for Python 3, I would use callable(). So, isinstance(x, (int, str, tuple)); but don't rely on isinstance for function. Its just not appropriate, almost universally, to really be that specific. When someone esays they want to accept a function, what they *really* mean in my experience is they want some sort of object that you can put ()'s on after, and usually with some sort of agreement: it'll accept X args, and return Y things. You can't readily test for those agreements, but you can test to see if it'll accept ()'s after and be all function-y. Doing callable(ff) will do that for you. -- ... Stephen Hansen ... Also: Ixokai ... Mail: me+list/python (AT) ixokai (DOT) io ... Blog: http://meh.ixokai.io/ P.S. The removal of callable is something I don't understand in Python 3: while generally speaking I do really believe and use duck typing, I too have on occassion wanted to dispatch based on 'is callable? do x'. Sometimes its not convenient to do so via duck typing. Its rare. But it is there. That isinstance()/issubclass got a boost in power with the ABC's and registering, while at the same time the ability to introspect about the function-y callable-y ness of a function was removed? Makes no sense to me. But alas! -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On 6/27/2010 10:25 PM, Stephen Hansen wrote: > On 6/27/10 7:09 PM, Steven W. Orr wrote: >> So, my question is, what value can I use as the 2nd arg to isinstance >> to see if >> foo is a function? And while I'm on the subject, what types does >> isinstance not >> support? > > Does it have to be a function? -- There's quite a few things which are > function-y enough that you really should accept them even if they may > not be technically a /function/. Like a class instance with the __call__ > method defined wrapping a function as a decorator. Or a bound method, > really. > > In Python 2.x, you can use callable(fun) -- that goes away in Py3 > though. But personally, I think this is the wrong approach. Ok, you just asked great questions, and your questions were based on what I didn't tell you. I'm trying to teach myself about how __metaclass__ can be used as a substitute for LSD. ;-) So, instead of writing a class that does typechecking on its arguments at instantiation time, I'm writing a metaclass that allows the class to announce what sort of values it specifically will be expecting after instantiation. The model I'm using is something I've found that http://cleverdevil.org/computing/78/ So, the basic idea is >>> class Person(Enforcer): ...name = Field(str) ...age = Field(int) ...ff = Field(function) but there's no factory function called function. Does this help? > > I'm assuming you need to do some different sort of behavior based on if > its a str, tuple or list-- okay. > > But, personally-- at that point, I would just *assume* the argument is a > function. And call it. > > If it can't be called, its not a functiony-thing. You can either let > that traceback propagate, or just raise a TypeError "expected arg to be > a string, tuple, list or callable". > > Then again, similarly I almost never want to test for if somethings a > tuple or list. I'd rather use it as a sequence type and see if it works: > while there's not as many 'sequency-like-things' out there as there are > function-like-things, there's still quite a few. > > So personally, I'd check if its a string (can it be unicode or regular? > If so isinstance(x,basestring)). > > Then I'd try to use it as a sequence, doing whatever I woulda done with > it sequence-like. If that works, great. If not, I'd try to call it. > > Etc. > > Then again it does depend on just what you're *doing* with the arg being > passed in. > -- Time flies like the wind. Fruit flies like a banana. Stranger things have .0. happened but none stranger than this. Does your driver's license say Organ ..0 Donor?Black holes are where God divided by zero. Listen to me! We are all- 000 individuals! What if this weren't a hypothetical question? steveo at syslang.net -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
Steven W. Orr wrote: I need to test an argument for a few different types. I'm calling my function like this arf = MyFunc(list) What I want to do is to test for whether something is a string, tuple, list or function. It's that last one that's causing me a problem. if isinstance(arg, (str, tuple, list)): No problem, but there are a lot of types that the type function returns. If I have a simple function def foo(): pass type(foo) prints out So, my question is, what value can I use as the 2nd arg to isinstance to see if foo is a function? And while I'm on the subject, what types does isinstance not support? >>> def foo(): ... pass ... >>> import types >>> dir(types) ['BooleanType', 'BufferType', 'BuiltinFunctionType', 'BuiltinMethodType', 'ClassType', 'CodeType', 'ComplexType', 'DictProxyType', 'DictType', 'DictionaryType', 'EllipsisType', 'FileType', 'FloatType', 'FrameType', 'FunctionType', 'GeneratorType', 'GetSetDescriptorType', 'InstanceType', 'IntType', 'LambdaType', 'ListType', 'LongType', 'MemberDescriptorType', 'MethodType', 'ModuleType', 'NoneType', 'NotImplementedType', 'ObjectType', 'SliceType', 'StringType', 'StringTypes', 'TracebackType', 'TupleType', 'TypeType', 'UnboundMethodType', 'UnicodeType', 'XRangeType', '__builtins__', '__doc__', '__file__', '__name__', '__package__'] >>> isinstance(f, types.FunctionType) True >>> And last, what is the correct way to do it if this is not the right way? Why do you want to know what type it is? Do you want to do different things depending on the type? If the same function can return instances of any number of unrelated types/classes, then there's something wrong in your design! (You should also learn what "duck typing" is!) :-) -- http://mail.python.org/mailman/listinfo/python-list
Re: Need instruction on how to use isinstance
On 6/27/10 7:09 PM, Steven W. Orr wrote: So, my question is, what value can I use as the 2nd arg to isinstance to see if foo is a function? And while I'm on the subject, what types does isinstance not support? Does it have to be a function? -- There's quite a few things which are function-y enough that you really should accept them even if they may not be technically a /function/. Like a class instance with the __call__ method defined wrapping a function as a decorator. Or a bound method, really. In Python 2.x, you can use callable(fun) -- that goes away in Py3 though. But personally, I think this is the wrong approach. I'm assuming you need to do some different sort of behavior based on if its a str, tuple or list-- okay. But, personally-- at that point, I would just *assume* the argument is a function. And call it. If it can't be called, its not a functiony-thing. You can either let that traceback propagate, or just raise a TypeError "expected arg to be a string, tuple, list or callable". Then again, similarly I almost never want to test for if somethings a tuple or list. I'd rather use it as a sequence type and see if it works: while there's not as many 'sequency-like-things' out there as there are function-like-things, there's still quite a few. So personally, I'd check if its a string (can it be unicode or regular? If so isinstance(x,basestring)). Then I'd try to use it as a sequence, doing whatever I woulda done with it sequence-like. If that works, great. If not, I'd try to call it. Etc. Then again it does depend on just what you're *doing* with the arg being passed in. -- ... Stephen Hansen ... Also: Ixokai ... Mail: me+list/python (AT) ixokai (DOT) io ... Blog: http://meh.ixokai.io/ -- http://mail.python.org/mailman/listinfo/python-list
