Re: Know if a object member is a method
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Hi Luca, use type(something).__name__ , e.g. def x(): pass class C: pass c = C() type(x).__name__ == 'function' True type(C).__name__ == 'classobj' True type(c).__name__ == 'instance' True On Sep 1, 2008, at 10:43 AM, Luca wrote: Hi all. I think this is a newbie question... what is the best method to know if a property of an object is a function? I'm thinking something as if type(obj.methodName)==??? Can someone help me? -- -- luca -- http://mail.python.org/mailman/listinfo/python-list -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (Darwin) iD8DBQFIu606cZ70OCIgLecRAhE6AJ4r0GuHlWxXbLaYuolqpJStYPD+ggCgidKg qtgl+nbaKgH5AoelTu5WeJU= =W4eG -END PGP SIGNATURE- -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
On Mon, 01 Sep 2008 10:43:25 +0200, Luca wrote: Hi all. I think this is a newbie question... what is the best method to know if a property of an object is a function? I'm thinking something as if type(obj.methodName)==??? Can someone help me? That's not quite as easy as you might think. In my testing, calling type(obj.methodName) can give any of the following: type 'instancemethod' type 'function' type 'builtin_function_or_method' There may be others as well. Possibly all you really need is to check if the attribute is callable without caring what type of method or function it is: callable(obj.methodName) True In my opinion, that's the best way. If you are sure that the method won't have side-effects or bugs: try: ... obj.method() ... except: ... print Not a method ... (But how can you be sure?) If you insist on an explicit test, try this: import new type(obj.methodName) == new.instancemethod or alternatively: isinstance(obj.methodName, new.instancemethod) True -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
On Mon, 01 Sep 2008 10:52:10 +0200, Manuel Ebert wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Hi Luca, use type(something).__name__ , e.g. def x(): pass class C: pass c = C() type(x).__name__ == 'function' True type(C).__name__ == 'classobj' True type(c).__name__ == 'instance' True That's relatively fragile, since such names aren't reserved in any way. It's easy to fool a name comparison check with an accidental name collision: class function(object): # not a reserved name ... pass ... x = function() type(x).__name__ 'function' x() # must be a function then... Traceback (most recent call last): File stdin, line 1, in module TypeError: 'function' object is not callable But not so easy to fool a type check: type(x) == new.function False Of course that's not bullet-proof either. I leave it as an exercise to discover how you might break that piece of code. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
On Mon, Sep 1, 2008 at 11:35 AM, Steven D'Aprano [EMAIL PROTECTED] wrote: That's relatively fragile, since such names aren't reserved in any way. It's easy to fool a name comparison check with an accidental name collision: class function(object): # not a reserved name ... pass ... x = function() type(x).__name__ 'function' x() # must be a function then... Traceback (most recent call last): File stdin, line 1, in module TypeError: 'function' object is not callable But not so easy to fool a type check: type(x) == new.function False Of course that's not bullet-proof either. I leave it as an exercise to discover how you might break that piece of code. Ok, so... What is the best way to do this? The most pythonic? -- -- luca -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
On Mon, 01 Sep 2008 11:45:36 +0200, Luca wrote: But not so easy to fool a type check: type(x) == new.function False Of course that's not bullet-proof either. I leave it as an exercise to discover how you might break that piece of code. Ok, so... What is the best way to do this? The most pythonic? The most pythonic might be not checking at all but simply *call* the object and deal with possible failures. What's your use case? Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
Luca wrote: On Mon, Sep 1, 2008 at 11:35 AM, Steven D'Aprano [EMAIL PROTECTED] wrote: ... But not so easy to fool a type check: type(x) == new.function False Of course that's not bullet-proof either. I leave it as an exercise to discover how you might break that piece of code. Ok, so... What is the best way to do this? The most pythonic? The question would be - why do you want this? Is it just curiosity or can we find a better solution to the overall problem, once understood? Regards Tino smime.p7s Description: S/MIME Cryptographic Signature -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
On Mon, 01 Sep 2008 11:45:36 +0200, Luca asked about recognizing methods: What is the best way to do this? The most pythonic? That depends on why you are doing it, and what you want to do with the information once you've found it. If you are experimenting in the interactive interpreter, the easiest way is simply call the method and see what happens: obj.methodName() # call the method If it succeeds, then it is some sort of callable, a method or a function or something more unusual. If you fear side-effects, then use: callable(obj.methodName) Alternatively, you can read the docs: help(obj) help(obj.methodName) If your aim is to write something like a debugger, profiler, or some other application that needs to inspect arbitrary objects and work out what they do, then you probably should be using: isinstance(obj.methodName, new.instancemethod) But remember that not all callable attributes are instancemethods! There is no one right way of doing this. Hope this helps. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
On Mon, Sep 1, 2008 at 2:18 PM, Steven D'Aprano [EMAIL PROTECTED] wrote: If your aim is to write something like a debugger, profiler, or some other application that needs to inspect arbitrary objects and work out what they do, then you probably should be using: isinstance(obj.methodName, new.instancemethod) But remember that not all callable attributes are instancemethods! There is no one right way of doing this. Hope this helps. Yes, this helps a lot. In facts I need to do something like a language parser. Thanks all. -- -- luca -- http://mail.python.org/mailman/listinfo/python-list
Re: Know if a object member is a method
Luca wrote: Yes, this helps a lot. In facts I need to do something like a language parser. a *parser* that works on object structures created by executing a Python program? /F -- http://mail.python.org/mailman/listinfo/python-list
