现在需要从另一个文件中调用类中的方法时，如何重写该函数？

Question

Here is the function (it's in a file, "worldmodel.py"):

def add_entity(world, entity):
   pt = entities.get_position(entity)
   if within_bounds(world, pt):
      old_entity = occ_grid.get_cell(world.occupancy, pt)
      if old_entity != None:
         entities.clear_pending_actions(old_entity)
      occ_grid.set_cell(world.occupancy, pt, entity)
      world.entities.append(entity)

And here is the class in a file named, "occ_grid.py":

class Grid:
   def __init__(self, width, height, occupancy_value):
      self.width = width
      self.height = height
      self.cells = []

      # initialize grid to all specified occupancy value
      for row in range(0, self.height):
         self.cells.append([])
         for col in range(0, self.width):
            self.cells[row].append(occupancy_value)

   def set_cell(self, point, value):
      self.cells[point.y][point.x] = value

My question is, how would I rewrite the line of code in "def add_entity" that refers to "set_cell"? (Now that I've made set_cell a method of the class Grid) NOTE: Before I made set_cell part of the grid class, it was a function outside of the class (but still in the same file as the class) Thanks!

Answer 1

You'll need to import occ_grid in your worldmodel.py , then instantiate a Grid object and call that objects set_cell() -method. The add_entity needs to get the Grid -object as its parameter unless it can safely instantiate new ones at will.

Here's a naive example which does not work but demonstrates what I mean:

import occ_grid

g = occ_grid.Grid(your_width, your_height, occupancy)

def add_entity(world, entity, grid):
    pt = entities.get_position(entity)
    if within_bounds(world, pt):
        old_entity = grid.get_cell(world.occupancy, pt)
        if old_entity != None:
            entities.clear_pending_actions(old_entity)
        grid.set_cell(world.occupancy, pt, entity)
        world.entities.append(entity)

add_entity(world, entity, g)

Answer 2

There are two issues here, (1) calling functions across modules and (2) calling methods of classes. It seems you can already do (1).

The trick is that although methods are defined as

 def methodName(self, ...)

They are called as

 object.methodName(...)

And object implicitly becomes the "self" Parameter. Here is an example:

import occ_grid  # Import the module (file) that contains Grid.
   .
   .   
world.occupancy = occ_grid.Grid()  # Create an instance of Grid.
   .
   .
def add_entity(world, entity):
   pt = entities.get_position(entity)       
   .
   .   
   world.occupancy.set_cell(pt, entity)

In this example, grid is a global variable, which is probably not a good design. I guess it should be a property of world , but that's only a guess.

Answer 3

Unless you make the set_cell function a static method of the Grid class, you're going to need and instance of Grid .

from occ_grid import Grid

I am going to make an assumption here, and say that your want your grid to be part of the world? Either way, this is an example of instantiating that class.

class World:
    grid = Grid()

    def add_entity(world, entity):
        # All that other stuff.
        world.grid.set_cell(pt, entity)