Re: Identifying a class type - bad practice?
James Harris wrote: I don't know yet whether it will be easier to modify the tree or to create a new one for each phase. You can create a new tree using this style as well. Just have each method create and return a new node instead of modifying the existing one. -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: Identifying a class type - bad practice?
On 18 Aug, 21:50, Chris Rebert c...@rebertia.com wrote: On Tue, Aug 18, 2009 at 10:09 AM, James Harrisjames.harri...@googlemail.com wrote: I am writing some code to form a tree of nodes of different types. The idea is to define one class per node type such as class node_type_1(node): specific properties by name including other node types class node_type_2(node): specific properties by name including other node types etc (Class node would hold any common properties). When walking the tree I need to know what type of node I'm dealing with so polymorphism isn't generally useful. The action to be taken depends on the node type. I'm sure it relates to the exact type of tree you're walking and the calculation you're doing on it, but what is the reason why your code, which in the abstract sounds like it will vaguely resemble this: def walk_tree(tree): if isinstance(tree, node_type_1): #code walk_tree(subtree) elif isinstance(tree, node_type_2): #code walk_tree(subtree) #etc... can't be written instead as: class node_type_1: def walk_tree(self): #code self.subtree.walk() class node_type_2: def walk_tree(self): #code self.subtree.walk() #etc Interesting idea. This may be a better and a more OO solution than what I had in mind. I'm not sure if I can use this but I'll see how it fits in as the work progresses. The tree is for a compiler. Initially the tree is for parsing of source code. Then it will need to be processed and changed as further compiler phases are written. I don't know yet whether it will be easier to modify the tree or to create a new one for each phase. So I guess whether I use the idea depends on the commonality of operations. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Identifying a class type - bad practice?
James Harris a écrit : On 18 Aug, 21:50, Chris Rebert c...@rebertia.com wrote: (snip) class node_type_1: def walk_tree(self): #code self.subtree.walk() class node_type_2: def walk_tree(self): #code self.subtree.walk() #etc Interesting idea. Basic OO stuff, really. I'd say it's even the whole point of OO. (snip) The tree is for a compiler. Initially the tree is for parsing of source code. Then it will need to be processed and changed as further compiler phases are written. I don't know yet whether it will be easier to modify the tree or to create a new one for each phase. So I guess whether I use the idea depends on the commonality of operations. You may want to have a look at the composite and visitor design patterns. AST are canonical use case for these patterns. HTH -- http://mail.python.org/mailman/listinfo/python-list
Identifying a class type - bad practice?
I am writing some code to form a tree of nodes of different types. The idea is to define one class per node type such as class node_type_1(node): specific properties by name including other node types class node_type_2(node): specific properties by name including other node types etc (Class node would hold any common properties). When walking the tree I need to know what type of node I'm dealing with so polymorphism isn't generally useful. The action to be taken depends on the node type. Two options appear to be useful: __class__ and isinstance. I know the latter will match the instance against any superclass and the former will match one class only. My question is: is this the Pythonic way to deal with such a tree? Is there a better way? In C I would use structs where one field was a tag indicating the kind of struct. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Identifying a class type - bad practice?
James Harris wrote: I am writing some code to form a tree of nodes of different types. The idea is to define one class per node type such as class node_type_1(node): specific properties by name including other node types class node_type_2(node): specific properties by name including other node types etc (Class node would hold any common properties). When walking the tree I need to know what type of node I'm dealing with so polymorphism isn't generally useful. The action to be taken depends on the node type. Two options appear to be useful: __class__ and isinstance. I know the latter will match the instance against any superclass and the former will match one class only. My question is: is this the Pythonic way to deal with such a tree? Is there a better way? In C I would use structs where one field was a tag indicating the kind of struct. James I would recommend going with isinstance. An instance of node_type_2 will not be an instance node_type_1, so no worries there, and it leaves open the option of subclassing further if you need to later on. ~Ethan~ -- http://mail.python.org/mailman/listinfo/python-list
Re: Identifying a class type - bad practice?
On Aug 18, 2:09 pm, James Harris james.harri...@googlemail.com wrote: I am writing some code to form a tree of nodes of different types. The idea is to define one class per node type such as class node_type_1(node): specific properties by name including other node types class node_type_2(node): specific properties by name including other node types etc (Class node would hold any common properties). When walking the tree I need to know what type of node I'm dealing with so polymorphism isn't generally useful. The action to be taken depends on the node type. Two options appear to be useful: __class__ and isinstance. I know the latter will match the instance against any superclass and the former will match one class only. My question is: is this the Pythonic way to deal with such a tree? Is there a better way? In C I would use structs where one field was a tag indicating the kind of struct. James I would probably go with hasattr(instance, 'what_I_want') André -- http://mail.python.org/mailman/listinfo/python-list
Re: Identifying a class type - bad practice?
On Tue, Aug 18, 2009 at 10:09 AM, James Harrisjames.harri...@googlemail.com wrote: I am writing some code to form a tree of nodes of different types. The idea is to define one class per node type such as class node_type_1(node): specific properties by name including other node types class node_type_2(node): specific properties by name including other node types etc (Class node would hold any common properties). When walking the tree I need to know what type of node I'm dealing with so polymorphism isn't generally useful. The action to be taken depends on the node type. I'm sure it relates to the exact type of tree you're walking and the calculation you're doing on it, but what is the reason why your code, which in the abstract sounds like it will vaguely resemble this: def walk_tree(tree): if isinstance(tree, node_type_1): #code walk_tree(subtree) elif isinstance(tree, node_type_2): #code walk_tree(subtree) #etc... can't be written instead as: class node_type_1: def walk_tree(self): #code self.subtree.walk() class node_type_2: def walk_tree(self): #code self.subtree.walk() #etc ? Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
