[Tutor] Class Nesting
Hello List, My name is Greg, and while working on a project I've come across a rather interesting problem. I'm trying to create a rough model of a star cluster and all of the stars and planets contained within. Kind of a cool project; hopefully it should work a little like this. I create a Star Cluster object, which goes through a list of positions and decides if it should build a Star System there. If it does, it then creates a Star System object at that position which in turn calls upon and creates several Planet objects to reside inside of it. All in all, about 64 positions to check, on average 24 Star Systems, each with between 2 and 9 planets. So here is the problem, to create an object, you need to assign it to a variable, and you need to know what that variable is to call upon it later, so to have a object build a second object, it would need to somehow create a variable name, and you would somehow have to know what name it picked. Unless perhaps you had a Star Cluster list which had all of your created Star System objects, each with their own list of Planets which you could use list to call upon maybe I have a general grasp on the idea of nesting and calling upon objects which you don't know the name of, but this goes far beyond my level of understanding. Can anyone shed some light on how this would work, or perhaps point me in the right direction of some documentation on this? Thanks for the help, and I hope this is not too difficult of a question. Greg ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Class Nesting
On 02/06/2012 08:17 PM, Greg Nielsen wrote: Hello List, My name is Greg, and while working on a project I've come across a rather interesting problem. I'm trying to create a rough model of a star cluster and all of the stars and planets contained within. Kind of a cool project; hopefully it should work a little like this. I create a Star Cluster object, which goes through a list of positions and decides if it should build a Star System there. If it does, it then creates a Star System object at that position which in turn calls upon and creates several Planet objects to reside inside of it. All in all, about 64 positions to check, on average 24 Star Systems, each with between 2 and 9 planets. So here is the problem, to create an object, you need to assign it to a variable, and you need to know what that variable is to call upon it later, so to have a object build a second object, it would need to somehow create a variable name, and you would somehow have to know what name it picked. Unless perhaps you had a Star Cluster list which had all of your created Star System objects, each with their own list of Planets which you could use list to call upon maybe I have a general grasp on the idea of nesting and calling upon objects which you don't know the name of, but this goes far beyond my level of understanding. Can anyone shed some light on how this would work, or perhaps point me in the right direction of some documentation on this? Thanks for the help, and I hope this is not too difficult of a question. Greg Since you talk of creating a StarCluster object, presumably you know how to make a class. So in the class definition, you can define attributes that each instance has. One of those attributes can be a list. So the list has a name, but not the individual items in the list. Generally, it's best to create an empty list attribute in the initializer of the class. Then whatever class method wants to create these items can simply append them to the list. At this point, you should write some code, and it'll either work, or you'll tell us what part of it you can't understand. -- DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Class Nesting
On Mon, Feb 06, 2012 at 08:17:05PM -0500, Greg Nielsen wrote: [...] So here is the problem, to create an object, you need to assign it to a variable, and you need to know what that variable is to call upon it later, so to have a object build a second object, it would need to somehow create a variable name, and you would somehow have to know what name it picked. Unless perhaps you had a Star Cluster list which had all of your created Star System objects, each with their own list of Planets which you could use list to call upon maybe Yes, that's exactly the way to do it. Rather than assigning each object to a name: cluster1 = StarCluster() cluster2 = StarCluster() ... you can work with a list of clusters: clusters = [StarCluster(), StarCluster(), ...] You can then operate on then one at a time. Say you want to do something to the 3rd cluster. Remembering that Python starts counting positions at zero, you would write something like: clusters[2].name = Local Cluster 12345 # give the cluster a name If your StarCluster objects are mutable (and if you don't know what that means, don't worry about it, by default all classes are mutable), you can grab a temporary reference to a cluster while working on it: for cluster in clusters: # work on each one sequentially if cluster.stars == []: print(Cluster %s has no stars. % cluster.name) Here I have assumed that each cluster is given a list of stars. Something like this: class StarCluster(object): def __init__(self): self.name = no name yet self.stars = [] def add_star(self, *args, **kw_args): self.stars.append(Star(*args, **kw_args)) Here I have given the StarCluster a method, add_star, which takes an arbitrary set of arguments, passes them on to the Star class, and adds the resultant star to the list. class Star(object): def __init__(self, name=no name yet, kind=red giant, planets=None): if planets is None: planets = [] self.planets = planets self.name = name self.kind = kind sol = Star( Sol, yellow dwarf, ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune'] # ha ha, Pluto can bite me ) I hope this helps, -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
