Tkinter:返回self.func（*args）错误（屏幕截图工具）

Question

python新手，我的代码不起作用。花时间检查以前出现的错误，一旦我解决了这些错误，我认为会很好。目标是截图，然后询问用户在哪里保存文件

代码：

from tkinter import *
import tkinter.messagebox
import tkinter.filedialog
import pyautogui

import datetime

def file_save():
    f = tkinter.filedialog.asksaveasfile(mode='w', defaultextension=".txt")
    if f is None: # asksaveasfile return `None` if dialog closed with "cancel".
        return
    text2save = str(Text(root).get(1.0, END)) # starts from `1.0`, not `0.0`
    f.write(text2save)
    f.close() # `()` was missing.



class Application():
    

    
    def __init__(self, master):
        self.master = master
        self.rect = None
        self.x = self.y = 0
        self.start_x = None
        self.start_y = None
        self.curX = None
        self.curY = None

        # root.configure(background = 'red')
        # root.attributes("-transparentcolor","red")

        root.attributes("-transparent", "white")
        root.geometry('400x50+200+200')  # set new geometry
        root.title('Snipping Bean')
        self.menu_frame = Frame(master, bg="blue")
        self.menu_frame.pack(fill=BOTH, expand=YES)

        self.buttonBar = Frame(self.menu_frame,bg="white")
        self.buttonBar.pack(fill=BOTH,expand=YES)

        self.snipButton = Button(self.buttonBar, width=10, command=self.createScreenCanvas, background="blue")
        self.snipButton.pack(expand=YES)

        self.master_screen = Toplevel(root)
        self.master_screen.withdraw()
        self.master_screen.attributes("-transparent", "blue")
        self.picture_frame = Frame(self.master_screen, background = "blue")
        self.picture_frame.pack(fill=BOTH, expand=YES)

    def takeBoundedScreenShot(self, x1, y1, x2, y2):
        im = pyautogui.screenshot(region=(x1, y1, x2, y2))
        fileName = file_save
        im.save(fileName + ".png")


    
    def createScreenCanvas(self):
        self.master_screen.deiconify()
        root.withdraw()

        self.screenCanvas = Canvas(self.picture_frame, cursor="cross", bg="grey11")
        self.screenCanvas.pack(fill=BOTH, expand=YES)

        self.screenCanvas.bind("<ButtonPress-1>", self.on_button_press)
        self.screenCanvas.bind("<B1-Motion>", self.on_move_press)
        self.screenCanvas.bind("<ButtonRelease-1>", self.on_button_release)

        self.master_screen.attributes('-fullscreen', True)
        self.master_screen.attributes('-alpha', .3)
        self.master_screen.lift()
        self.master_screen.attributes("-topmost", True)

    def on_button_release(self, event):
        self.recPosition()

        if self.start_x <= self.curX and self.start_y <= self.curY:
            print("right down")
            self.takeBoundedScreenShot(self.start_x, self.start_y, self.curX - self.start_x, self.curY - self.start_y)

        elif self.start_x >= self.curX and self.start_y <= self.curY:
            print("left down")
            self.takeBoundedScreenShot(self.curX, self.start_y, self.start_x - self.curX, self.curY - self.start_y)

        elif self.start_x <= self.curX and self.start_y >= self.curY:
            print("right up")
            self.takeBoundedScreenShot(self.start_x, self.curY, self.curX - self.start_x, self.start_y - self.curY)

        elif self.start_x >= self.curX and self.start_y >= self.curY:
            print("left up")
            self.takeBoundedScreenShot(self.curX, self.curY, self.start_x - self.curX, self.start_y - self.curY)

        self.exitScreenshotMode()
        return event

    def exitScreenshotMode(self):
        print("Screenshot mode exited")
        self.screenCanvas.destroy()
        self.master_screen.withdraw()
        root.deiconify()

    def exit_application(self):
        print("Application exit")
        root.quit()

    def on_button_press(self, event):
        # save mouse drag start position
        self.start_x = self.screenCanvas.canvasx(event.x)
        self.start_y = self.screenCanvas.canvasy(event.y)

        self.rect = self.screenCanvas.create_rectangle(self.x, self.y, 1, 1, outline='', width=1, fill="blue")

        
    def on_move_press(self, event):
        self.curX, self.curY = (event.x, event.y)
        # expand rectangle as you drag the mouse
        self.screenCanvas.coords(self.rect, self.start_x, self.start_y, self.curX, self.curY)

    def recPosition(self):
        print(self.start_x)
        print(self.start_y)
        print(self.curX)
        print(self.curY)

if __name__ == '__main__':
    root = Tk()
    app = Application(root)
    root.iconbitmap(default='transparent.ico')
    root.mainloop()

程序运行，但一旦要拍摄屏幕截图，它就会停止工作

我得到的错误是

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.9_3.9.2032.0_x64__qbz5n2kfra8p0\lib\tkinter\__init__.py", line 1892, in __call__
    return self.func(*args)
  File "c:\Users\username\Downloads\Coding Shite\Screenshot.py", line 80, in on_button_release
    self.takeBoundedScreenShot(self.start_x, self.start_y, self.curX - self.start_x, self.curY - self.start_y)
  File "c:\Users\username\Downloads\Coding Shite\Screenshot.py", line 55, in takeBoundedScreenShot
    im.save(fileName + ".png")
TypeError: unsupported operand type(s) for +: 'function' and 'str'