如何在 python 中使用一个变量从一个 class 到另一个变量？

Question

I am new to Python and I am trying to use a variable from one class in to another class, but onfortunately I dont understand how to do it.

I have written the code below. Inside de World class I have a while loop with inside the loop ther is deltaTime. I want to pass deltaTime to the class test where i use deltaTime * 2.

How can I do that?

I have searched around but I didn't understand the explanation.

import time as tm

class Test():
  def __init__(self):
    self.v = 10

    v += 'here I need the deltaTime that is inside the while loop in the world class ''self.deltaTime' * 2
    print(v)

Here is class world

class World():
    def __init__(self):
        self.test = Test(self)

    def run (self):
        while True:                 # Main real-time simulation loop
            # BEGIN mandatory statements
            self.oldTime = self.time
            self.time = tm.time ()  # The only place where the realtime clock is repeatedly queried
            self.deltaTime = self.time - self.oldTime
            # END mandatory statements
            
            # ... other code, using objects that are in the world, like a racetrack and cars
            
            print ('deltaTime ', self.deltaTime)
            self.screen.update ()
            tm.sleep (0.02)         # Needed to free up processor for other tasks like I/O

world = World ()

world.run ()

Answer 1

You're passing the self to Test when you do self.test = Test(self) . But you didn't add that as a parameter in the Test.__init__ method. It should be:

class Test():
    def __init__(self, world):
        self.v = 10
        self.world = world

        self.v += world.deltaTime * 2
        print(v)

But When you call Test(self) , you haven't filled in self.deltaTime yet. You should use it from a different method in the Test class, that you call from the while loop.

class Test():

    def __init__(self, world):
        self.v = 10
        self.world = world

    def display_time(self):
        self.v += world.deltaTime * 2
        print(self.v)

Then call test.display_time() from World.run()

Answer 2

You need to create the Test object in the code:

t_object = Test(...)

and insert the object to the run function:

def run(self, t_object):

and then each time you want to increment the v value you can just increment the attribute:

t_object.v += self.deltaTime
print(t_object.v)

so the lines here is not needed:

v += 'here I ne ... 
print(v)

**In fact, it's wrong to do it as you did with these 2 lines.. cus it's not updating the attribute but a new variable name v.

** There is also no need to put () after the class name if there is no inheritance. in this case, only this way is ok:

class Name:

Answer 3

I think you're talking about class composition .

import time as tm

class Test():
  def __init__(self):
    self.v = 10

  def use_world_deltatime(self, delta_time):
    v += self.deltaTime * 2
    print(v)

class World():
    def __init__(self):
        self.test = Test()

    def run (self):
        while True:                 # Main real-time simulation loop
            # BEGIN mandatory statements
            self.oldTime = self.time
            self.time = tm.time ()  # The only place where the realtime clock is repeatedly queried
            self.deltaTime = self.time - self.oldTime
            # END mandatory statements
            
            # ... other code, using objects that are in the world, like a racetrack and cars
            self.test.use_world_deltatime(self.deltaTime)
            print ('deltaTime ', self.deltaTime)
            self.screen.update ()
            tm.sleep (0.02)         # Needed to free up processor for other tasks like I/O

world = World()

world.run()

Basically, you create the Test class as an independent object and instantiate it inside the World class. Once you do this, you may use Test's methods (like the use_world_deltatime ) whenever you like.

Does it make sense?