1、编写一个Line Length应用程序 要求如下：在窗体上绘制一条黑色直线并计算他的长度，如图所示。该直线从按下鼠标按钮出的坐标开始，直到释放鼠标按钮的那点结束。应用程序应当在“Length = ”标签中显示直线的长度（即两个端点之间的距离）。

以下是使用Python和Tkinter库编写的Line Length应用程序代码，满足您的需求：

import tkinter as tk
import math

class LineLengthApp:
    def __init__(self, master):
        self.master = master
        master.title("Line Length App")

        self.start_x = None
        self.start_y = None
        self.end_x = None
        self.end_y = None

        self.canvas = tk.Canvas(master, width=400, height=400, bg="white")
        self.canvas.pack()

        self.canvas.bind("<Button-1>", self.on_click)
        self.canvas.bind("<B1-Motion>", self.on_drag)
        self.canvas.bind("<ButtonRelease-1>", self.on_release)

        self.length_label = tk.Label(master, text="Length = 0")
        self.length_label.pack()

    def on_click(self, event):
        self.start_x = event.x
        self.start_y = event.y

    def on_drag(self, event):
        self.canvas.delete("line")
        self.end_x = event.x
        self.end_y = event.y
        self.canvas.create_line(self.start_x, self.start_y, self.end_x, self.end_y, width=2, tag="line")

    def on_release(self, event):
        self.canvas.delete("line")
        self.end_x = event.x
        self.end_y = event.y
        length = math.sqrt((self.end_x - self.start_x)**2 + (self.end_y - self.start_y)**2)
        self.length_label.config(text="Length = {:.2f}".format(length))

root = tk.Tk()
app = LineLengthApp(root)
root.mainloop()

运行该程序后，会在窗口上显示一个白色的画布，您可以在上面按下鼠标左键并拖动，画出一条直线，直到松开鼠标左键。程序会在窗口上方显示一条标签，标识出该直线的长度。