When to use "property" builtin: auxiliary functions and generators
- by Seth Johnson
I recently discovered Python's property built-in, which disguises class method getters and setters as a class's property. I'm now being tempted to use it in ways that I'm pretty sure are inappropriate.
Using the property keyword is clearly the right thing to do if class A has a property _x whose allowable values you want to restrict; i.e., it would replace the getX() and setX() construction one might write in C++.
But where else is it appropriate to make a function a property? For example, if you have
class Vertex(object):
def __init__(self):
self.x = 0.0
self.y = 1.0
class Polygon(object):
def __init__(self, list_of_vertices):
self.vertices = list_of_vertices
def get_vertex_positions(self):
return zip( *( (v.x,v.y) for v in self.vertices ) )
is it appropriate to add
vertex_positions = property( get_vertex_positions )
?
Is it ever ok to make a generator look like a property? Imagine if a change in our code meant that we no longer stored Polygon.vertices the same way. Would it then be ok to add this to Polygon?
@property
def vertices(self):
for v in self._new_v_thing:
yield v.calculate_equivalent_vertex()
