I have recently stated trying to use the newer style of classes in Python (those derived from object). As an excersise to familiarise myself with them I am trying to define a class which has a number of class instances as attributes, with each of these class instances describing a different type of data, e.g. 1d lists, 2d arrays, scalars etc. Essentially I wish to be able to write
some_class.data_type.some_variable
where data_type
is a class instance describing a collection of variables. Below is my first attempt at implementing this, using just a profiles_1d
instance and rather generic names:
class profiles_1d(object):
def __init__(self, x, y1=None, y2=None, y3=None):
self.x = x
self.y1 = y1
self.y2 = y2
self.y3 = y3
class collection(object):
def __init__(self):
self._profiles_1d = None
def get_profiles(self):
return self._profiles_1d
def set_profiles(self, x, *args, **kwargs):
self._profiles_1d = profiles_1d(x, *args, **kwargs)
def del_profiles(self):
self._profiles_1d = None
profiles1d = property(fget=get_profiles, fset=set_profiles, fdel=del_profiles,
doc="One dimensional profiles")
Is the above code roughly an appropriate way of tackling this problem. The examples I have seen of using property
just set the value of some variable. Here I require my set method to initialise an instance of some class. If not, any other suggestions of better ways to implement this would be greatly appreciated.
In addition, is the way I am defining my set method ok? Generally the set method, as far as I understand, defines what to do when the user types, in this example,
collection.profiles1d = ...
The only way I can correctly set the attributes of the profiles_1d
instance with the above code is to type collection.set_profiles([...], y1=[...], ...)
, but I think that I shouldn't be directly calling this method. Ideally I would want to type collection.profiles = ([...], y1=[...], ...)
: is this correct/possible?
Finally, I have seen a decorators mentioned alot with repect to the new style of classes, but this is something I know very little about. Is the use of decorators appropriate here? Is this something I should know more about for this problem?
First, it's good you're learning new-style classes. They've got lots of advantages.
The modern way to make properties in Python is:
then set
profiles
by doingNotice all three methods having the same name.
This is not normally done; either have them pass the attributes to
collection
s constructor or have them create theprofiles_1d
themselves and then docollections.profiles = myprofiles1d
or pass it to the constructor.When you want the attribute to manage access to itself instead of the class managing access to the attribute, make the attribute a class with a descriptor. Do this if, unlike in the property example above, you actually want the data stored inside the attribute (instead of another, faux-private instance variable). Also, it's good for if you're going to use the same property over and over again -- make it a descriptor and you don't need to write the code multiple times or use a base class.
I actually like the page by @S.Lott -- Building Skills in Python's Attributes, Properties and Descriptors.