attribute of user-defined class can't change in applymethod animation

[ky0ha]

Situation:

I defined a class named CodeLine to load code from a file, create Code mobject for what i get. Then I add a arrow mobject to markup which line of those code are running (just like debug) to show the running process of the code.
I made some method for my class. CodeLine.move_up makes arrow to previous line of code, CodeLine.move_down makes arrow to next line of code. Looks like they actually work. Then I create a method named CodeLine.jump_to that I want to use this method to move arrow to specified row. Obviously, for this method, I must define a attribute to record current line number. When I jump to a line, current line number must be changed.
I use ApplyMethod and CodeLine.shift to move the arrow and change current line number at same time. But in this time, something wrong! The arrow moved but current line number wasn't changed. There are the part of origin code.

from manimlib import *

class CodeLine(VGroup):
    def __init__(self, code_path: str, **kwargs):
        self.code_path = code_path
        self.line_height = 0.306
        self.code_content, self.total_lines = self.load_code_file()
        self.code_mob = Code(self.code_content)
        self.arrow_mob = Arrow(self.code_mob.get_corner(LEFT) + LEFT, self.code_mob.get_corner(LEFT))
        if self.total_lines%2 == 0:
            self.arrow_mob.shift(DOWN * 0.145 + UP * self.line_height * (self.total_lines // 2))
        else:
            self.arrow_mob.shift(UP * self.line_height * (self.total_lines // 2))
        self.current_line_number = 1
        super().__init__(self.code_mob, self.arrow_mob)

    
    def load_code_file(self):
        with open(self.code_path) as f:
            content = f.readlines()
            total_lines = len(content)
            content = "".join(i for i in content)
            return (content, total_lines)
    
    def move_up(self):
        if self.current_line_number > 1:
            self.current_line_number -= 1
            return self.arrow_mob.shift(self.line_height * UP)
        else:
            log.warning(f"You can't move the arrow to previous line because persent line number" + \
                        f"is {self.current_line_number}.")
            return None
    
    def move_down(self):
        if self.current_line_number < self.total_lines:
            self.current_line_number += 1
            return self.arrow_mob.shift(self.line_height * DOWN)
        else:
            log.warning(f"You can't move the arrow to next line because persent line number" + \
                        f"is {self.current_line_number}.")
            return None
    
    def jump_to(self, line_number: int):
        if line_number <= self.total_lines or line_number >= 1:
            diff = line_number - self.current_line_number
            log.info(f"{line_number} - {self.current_line_number} = {diff}")
            self.current_line_number = line_number
            if diff<0:
                return self.arrow_mob.shift(UP * abs(diff) * self.line_height)
            elif diff>0:
                return self.arrow_mob.shift(DOWN * abs(diff) * self.line_height)
        else:
            log.warning(f"You can't jump to out of range of code lines number")
            return None

from manimlib import *
import mymoudle.coder as coder

class hello(Scene):
    def construct(self):
        codes = coder.CodeLine("test.py")
        # 0.29

        self.add(codes)
        self.wait(1)
        self.play(ApplyMethod(codes.jump_to, 4))
        self.play(ApplyMethod(codes.jump_to, 3))    # ! wrong

        self.embed()

What happend

self.current_line_number is not changed!
The first jump_to will move arrow to line 4, but the second will move arrow to line 6. The reason is when arrow moved, the arrtibute of self.current_line_number is not change to line_number. So the value of current_line_number still is 1 when second jump_to applied and it will cause that method think you want to move down the arrow 2 lines (diff = line_number - self.current_line_number is 2).

The reason what I found is...

I found the reason out! The reason is when ApplyMethod be called, it will create a copy of mobject, so, by the reason, the copy of CodeLine's attribute has been changed but not the origin CodeLine which we used.
For deal with it, I try to use class attributes instead of instance attributes. The code that be changed to...

from manimlib import *

class CodeLine(VGroup):
    current_line_number = 1    # * changed
    def __init__(self, code_path: str, **kwargs):
        self.code_path = code_path
        self.line_height = 0.306
        self.code_content, self.total_lines = self.load_code_file()
        self.code_mob = Code(self.code_content)
        self.arrow_mob = Arrow(self.code_mob.get_corner(LEFT) + LEFT, self.code_mob.get_corner(LEFT))
        if self.total_lines%2 == 0:
            self.arrow_mob.shift(DOWN * 0.145 + UP * self.line_height * (self.total_lines // 2))
        else:
            self.arrow_mob.shift(UP * self.line_height * (self.total_lines // 2))
        # self.current_line_number = 1    # * changed
        super().__init__(self.code_mob, self.arrow_mob)

    def load_code_file(self):
        with open(self.code_path) as f:
            content = f.readlines()
            total_lines = len(content)
            content = "".join(i for i in content)
            return (content, total_lines)
    
    def move_up(self):
        if self.current_line_number > 1:
            self.current_line_number -= 1
            return self.arrow_mob.shift(self.line_height * UP)
        else:
            log.warning(f"You can't move the arrow to previous line because persent line number" + \
                        f"is {self.current_line_number}.")
            return None
    
    def move_down(self):
        if self.current_line_number < self.total_lines:
            self.current_line_number += 1
            return self.arrow_mob.shift(self.line_height * DOWN)
        else:
            log.warning(f"You can't move the arrow to next line because persent line number" + \
                        f"is {self.current_line_number}.")
            return None
    
    def jump_to(self, line_number: int):
        if line_number <= self.total_lines or line_number >= 1:
            diff = line_number - self.current_line_number
            log.info(f"{line_number} - {self.current_line_number} = {diff}")
            CodeLine.current_line_number = line_number    # * changed
            if diff<0:
                return self.arrow_mob.shift(UP * abs(diff) * self.line_height)
            elif diff>0:
                return self.arrow_mob.shift(DOWN * abs(diff) * self.line_height)
        else:
            log.warning(f"You can't jump to out of range of code lines number")
            return None

By the way, problem has benn solved. But I don't think that is a good way, Because that will cause that I can't to create second CodeLine instance, the CodeLine become to a singleton class... That is too bad. But I can't find another way to avoid that problem...
What can I do? Can I change the manim's origin code to make it works? Or mine?