A First (Real) Example

https://tkdocs.com/tutorial/firstexample.html

 Code

from tkinter import *
from tkinter import ttk


def calculate(*args):
    try:
        value = float(feet.get())
        meters.set((0.3048 * value * 10000.0 + 0.5) / 10000.0)
    except ValueError:
        pass


root = Tk()
root.title("Feet to Meters")
mainframe = ttk.Frame(root, padding="3 3 12 12")
# mainframe = ttk.Frame(root)
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)
feet = StringVar()
meters = StringVar()
feet_entry = ttk.Entry(mainframe, width=7, textvariable=feet)
feet_entry.grid(column=2, row=1, sticky=(W, E))
ttk.Label(mainframe, textvariable=meters).grid(column=2, row=2, sticky=(W, E))
ttk.Button(mainframe, text="Calculate", command=calculate).grid(column=3, row=3,
                                                                sticky=W)
ttk.Label(mainframe, text="feet").grid(column=3, row=1, sticky=W)
ttk.Label(mainframe, text="is equivalent to").grid(column=1, row=2, sticky=E)
ttk.Label(mainframe, text="meters").grid(column=3, row=2, sticky=W)
for child in mainframe.winfo_children(): child.grid_configure(padx=5, pady=5)

for child in mainframe.winfo_children():
    print(child)
feet_entry.focus()
root.bind('<Return>', calculate)
root.mainloop()

FeetToMeters

from tkinter import *
from tkinter import ttk


class FeetToMeters:

    def __init__(self, root):
        root.title("Feet to Meters")
        mainframe = ttk.Frame(root, padding="3 3 12 12",relief="groove",borderwidth=3)  # padding=(左,上,右,下)
        mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
        root.columnconfigure(0, weight=1)
        root.rowconfigure(0, weight=1)

        self.feet = StringVar(value=1)
        feet_entry = ttk.Entry(mainframe, width=7, textvariable=self.feet)
        feet_entry.grid(column=2, row=1, sticky=(W, E))
        self.meters = StringVar()

        ttk.Label(mainframe, textvariable=self.meters).grid(column=2, row=2, sticky=(W, E))
        ttk.Button(mainframe, text="Calculate", command=self.calculate).grid(column=3, row=3, sticky=W)

        ttk.Label(mainframe, text="feet").grid(column=3, row=1, sticky=W)
        ttk.Label(mainframe, text="is equivalent to").grid(column=1, row=2, sticky=E)
        ttk.Label(mainframe, text="meters").grid(column=3, row=2, sticky=W)

        for child in mainframe.winfo_children():
            child.grid_configure(padx=5, pady=5)   # 各组件之间上下左右的间距为5 ;

        feet_entry.focus()  # 窗口打开后光标自动移动到 输入框 ;
        root.bind("<Return>", self.calculate)

    def calculate(self, *args):
        try:
            value = float(self.feet.get())
            self.meters.set(int(0.3048 * value * 10000.0 + 0.5) / 10000.0)
        except ValueError:
            pass


if __name__ == '__main__':
    root = Tk()
    FeetToMeters(root)
    root.mainloop()