Python中的动态对象实例化

Question

I'm having trouble finding out how to dynamically instantiate multiple instances of a class. For example, I'm given a file with an x,y,z and t coordinate on each line. I want to place each line into a class named Droplet that is uniquely identified bu the x,y because the z position and time varies with time. Each Droplet will have a hashtable that maps a time to az coordinate.

The big picture is that each line of input specifies a location of a water surface at a point in time and I will be animating this in Blender using python.

The part I'm having trouble with that I don't know how many instances of Droplet I will have to instantiate, so I can't do something like

drop1 = Droplet(0,0)
drop2 = Droplet(0,1)
... and so on

Is there a way for me to automate class instantiation using the unique x,y as an identifier in Python?

Answer 1

Yea just do it in a loop and put the objects into a list:

drops = []
for line in file:
    x, y, z, t = parseFromFile(line)
    drops.append(Droplet(x,y,z,t))

or, more Pythonesque:

drops = [Droplet(*parseFromFile(line)) for line in file]

* here takes the (presumbably four) values returned by parseFromFile and uses them as four arguments for the Droplet instantiation

Answer 2

If you need to uniquely identify them by the x and y direction (and, I guess, overwrite them when a new one with the same coordinates comes along), I'd use a 2-dimensional array indexed by x and y, and store the Droplet objects in that collection. So something like this:

droplets[x][y] = Droplet(x,y,z,t)

You'll have to read up on how to initialize 2-d arrays; you need to first make sure that droplets has enough room in both the x and y directions for all the droplets to fit in. But this way you can pick out any particular droplet you want by its x and y coordinate.

Answer 3

At a high level

drops = []
with open('drop_file.txt', 'r') as f:
    for line in f:
        x, y = line.strip().split()
        drops.append(Droplet(x, y))

then you can loop over the list of droplets when you need to do something to each of them.

this assumes that your file is in the format

xy

x1 y1