Re: group several methods under a attribute
In article mailman.3435.1239058603.11746.python-l...@python.org, Rhodri James rho...@wildebst.demon.co.uk wrote: You'll note that this is, all Aaron's protests to the contrary, splitting your class up into multiple cooperating classes. Ayup. If you're set on doing it like this, doing it this way avoids polluting your namespace so much: class ClsB(object): class ClsA(object): def do_something(self): print Here's A doing something def __init__(self): self.A = ClsB.ClsA() def do_something(self): print Here's B doing something Blech. The pollution caused by a separate class is minimal, and nested class definitions are likely to have problems (the most obvious is that pickling will break). -- Aahz (a...@pythoncraft.com) * http://www.pythoncraft.com/ Why is this newsgroup different from all other newsgroups? -- http://mail.python.org/mailman/listinfo/python-list
group several methods under a attribute
Hi, I'm working on a pretty large class and I'd like to group several methods under a attribute. Its not convenient to chop up the class in several smaller classes, nor would mixins really solve the issue. So, what is a pythonic way of grouping several methods under a attribute? Many thanks in advance, -jelle -- http://mail.python.org/mailman/listinfo/python-list
Re: group several methods under a attribute
jelle wrote: Hi, I'm working on a pretty large class Can you describe what its purpose is? and I'd like to group several methods under a attribute. That doesn't work in Python without bending the Python. Its not convenient to chop up the class in several smaller classes, But that's almost certainly the right thing to do. nor would mixins really solve the issue. So, what is a pythonic way of grouping several methods under a attribute? Whatever it is, you should find a better way instead of cramming everything into a single class. That smells of the God Object antipattern (http://en.wikipedia.org/wiki/God_object). -- Gerhard -- http://mail.python.org/mailman/listinfo/python-list
Re: group several methods under a attribute
Whatever it is, you should find a better way instead of cramming everything into a single class. That smells of the God Object antipattern (http://en.wikipedia.org/wiki/God_object). Thanks Gerard, I'll take your advice. -jelle -- http://mail.python.org/mailman/listinfo/python-list
Re: group several methods under a attribute
On Apr 6, 5:40 am, jelle jelleferi...@gmail.com wrote: Hi, I'm working on a pretty large class and I'd like to group several methods under a attribute. Its not convenient to chop up the class in several smaller classes, nor would mixins really solve the issue. So, what is a pythonic way of grouping several methods under a attribute? Many thanks in advance, -jelle Hi jelle, I disagree with Gerhard that you 'should find a better way' and another way 'almost certainly the right thing', unless his reason is merely that it's an advanced technique that will get you into problems down the road. There's nothing 'un-object-oriented' about it. The link to the God pattern alleges that it fails to 'divide and conquer', but you are dividing. I think Python opens some beautiful doors in this regard. Here is some code which I understand accomplishes what you sought. class ClsA( object ): def __init__( self ): self.inst= None def __get__( self, instance, owner ): self.inst= instance return self def submethA( self, arg ): print( 'submethA %r, instance %r'% ( arg, self.inst ) ) class ClsB( object ): A= ClsA( ) def methA( self, arg ): print( 'methA %r'% arg ) b= ClsB( ) b.methA( 'this' ) b.A.submethA( 'that' ) #Output: ''' methA 'this' submethA 'that', instance __main__.ClsB object... ''' In Python 3, you don't need 'ClsA' and 'ClsB' to inherit from 'object' explicitly. If you call 'b.A' from a class, 'ClsB.A', you will get a 'ClsA' object with a None 'inst' attribute, which is a big hole waiting for you to step in. Perhaps you want a wrapper for your methods of 'ClsA' to check that 'inst' is set, or merely throw an exception in '__get__' if 'instance' is 'None'. Python after all requires that a method's first argument be an instance of an improper subclass of the class it was defined for. -- http://mail.python.org/mailman/listinfo/python-list
Re: group several methods under a attribute
On Apr 6, 12:02 pm, Aaron Brady castiro...@gmail.com wrote: On Apr 6, 5:40 am, jelle jelleferi...@gmail.com wrote: Hi, I'm working on a pretty large class and I'd like to group several methods under a attribute. Its not convenient to chop up the class in several smaller classes, nor would mixins really solve the issue. So, what is a pythonic way of grouping several methods under a attribute? Many thanks in advance, -jelle Hi jelle, I disagree with Gerhard that you 'should find a better way' and another way 'almost certainly the right thing', unless his reason is merely that it's an advanced technique that will get you into problems down the road. snip class ClsA( object ): def __init__( self ): self.inst= None def __get__( self, instance, owner ): self.inst= instance return self snip There's a potential conflict in the above, which may have contributed to Gerhard's advice. If you have: bA= ClsB( ) bB= ClsB( ) bA.A.submethA( 'what' ) then the ClsA instance will think it's being accessed from 'bA' until it's accessed again! This may cause problems such as if you store a reference to it, because bB could access it, and it won't think it's being accessed from bA anymore. To get around this, you probably want '__get__' to create a new object that is specifically dedicated to the instance of ClsB that's calling it. bA.A and bB.A return new objects, separate from each other. However, then two calls to bA.A won't return the same object; they'll return new every time. Another detail is that ClsA can't store instance information. It should be stored in ClsB instances, and the methods merely go somewhere else. Otherwise, the right place for 'A= ClsA( )' is in the constructor: class clsB: def __init__( self ): self.A= ClsA( ) Then, every ClsB instance has its own instance of ClsA, and it can store instance information, and doesn't create new instances when you call it. The creation of 'ClsA' merely goes in the initializer, not the class statement. -- http://mail.python.org/mailman/listinfo/python-list
Re: group several methods under a attribute
Hi Aaron, Thanks a lot for your suggestions. I wasnt familiar with the __get__ magic, which seems interesting. So, finally it seems that the cleanest pattern is: class ClsA( object ): def __init__( self, other ): self.inst= other def submethA( self, arg ): print( 'submethA %r, instance %r'% ( arg, self.inst ) ) class ClsB( object ): def methA( self, arg ): self.A= ClsA( self ) print( 'methA %r'% arg ) b= ClsB( ) b.methA( 'this' ) b.A.submethA( 'that' ) Many thanks, -jelle -- http://mail.python.org/mailman/listinfo/python-list
Re: group several methods under a attribute
On Mon, 06 Apr 2009 20:52:50 +0100, jelle jelleferi...@gmail.com wrote: Hi Aaron, Thanks a lot for your suggestions. I wasnt familiar with the __get__ magic, which seems interesting. So, finally it seems that the cleanest pattern is: class ClsA( object ): def __init__( self, other ): self.inst= other def submethA( self, arg ): print( 'submethA %r, instance %r'% ( arg, self.inst ) ) class ClsB( object ): def methA( self, arg ): self.A= ClsA( self ) print( 'methA %r'% arg ) b= ClsB( ) b.methA( 'this' ) b.A.submethA( 'that' ) You'll note that this is, all Aaron's protests to the contrary, splitting your class up into multiple cooperating classes. If you're set on doing it like this, doing it this way avoids polluting your namespace so much: class ClsB(object): class ClsA(object): def do_something(self): print Here's A doing something def __init__(self): self.A = ClsB.ClsA() def do_something(self): print Here's B doing something b = ClsB() b.do_something() b.A.do_something() -- Rhodri James *-* Wildebeeste Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
