將tkinter輸入框的值變成浮點數（python）

Question

我是初學者。我已經嘗試了一切，以使下面的代碼將數字輸入輸入到輸入框中，並使用它們進行計算。我得到了ValueError，我沒有做任何事情讓這種停止發生。這應該是一個計算每月利息支付和支出總額的計劃。我把它放在一個簡單的產品上，直到我解決這個更基本的問題。謝謝。

def multiply(var1, var2, var3): 
    product = float(var1 * var2 * var3) 
    return product 


def btnClick(event): 
    x = float(entry.get()) 


main = Tk() 
main.title("Assignment 16") 

main.geometry("500x500") 
main["bg"] = "#000066" 

lblFirst = Label(main, text="Amount to Pay: ") 
lblFirst.grid(row=0, column=3, pady=5) 
entry = Entry(main, width=20) 
entry.grid(row=0, column=4) 
amount = entry.get() 
lblSecond = Label(main, text="Interest Rate (like 7.5): ") 
lblSecond.grid(row=2, column=3, pady=10) 
entry2 = Entry(main, width=20) 
entry2.grid(row=2, column=4) 
rate = entry2.get() 
lblThird = Label(main, text="Years to Pay: ") 
lblThird.grid(row=4, column=3, pady=15) 
entry3 = Entry(main, width=20) 
entry3.grid(row=4, column=4) 
years = entry3.get() 

try: 
    # Try to make it a float 
    if amount.isnumeric(): 
     amount = float(amount) 

except ValueError: 
    # Print this if the input cannot be made a float 
    print("Bad input") 

try: 
    # Try to make it a float 
    if rate.isnumeric(): 
     rate = float(rate) 

except ValueError: 
    # Print this if the input cannot be made a float 
    print("Bad input") 

try: 
    # Try to make it a float 
    if years.isnumeric(): 
     years = int(years) 

except ValueError: 
    # Print this if the input cannot be made a float 
    print("Bad input") 

lblFourth = Label(main, text="Monthly Payment: ") 
lblFourth.grid(row=6, column=3, pady=15) 
lblFourthTwo = Label(main, text="XXXXX") 
lblFourthTwo.grid(row=6, column=4) 
lblFifth = Label(main, text="Total of Paymenta: ") 
lblFifth.grid(row=8, column=3, pady=15) 
lblFifthTwo = Label(main, text="XXXXX") 
lblFifthTwo.grid(row=8, column=4) 

button1 = Button(main, text='Convert', width=10, command=btnClick) 
button2 = Button(main, text='Calculate', width=10, command=multiply(amount, rate, years)) 
button1.grid(padx=20, pady=20) 

main.mainloop() 

Answer 1

你所有的代碼運行之前的mainloop開始。

使用GUI工具包（如tkinker）的程序是事件驅動的。您的代碼只有在主循環之前在設置中運行，然後在事件處理程序中運行。

您可以使用驗證來確保只輸入數字。

下面的工作示例（用於Python 3）。這也顯示瞭如何從事件處理程序中的編輯框中獲取值以及如何創建合成事件來更新其他小部件。

import tkinter as tk 
from tkinter import ttk 

# Creating and placing the widgets 
root = tk.Tk() 
root.wm_title('floating point entry') 
qedit = ttk.Entry(root, justify='right') 
qedit.insert(0, '100') 
qedit.grid(row=0, column=0, sticky='ew') 
result = ttk.Label(root, text='100') 
result.grid(row=1, column=0) 
ttk.Button(root, text="Exit", command=root.quit).grid(row=2, column=0) 


# Callback functions 
def is_number(data): 
    if data == '': 
     return True 
    try: 
     float(data) 
     print('value:', data) 
    except ValueError: 
     return False 
    result.event_generate('<<UpdateNeeded>>', when='tail') 
    return True 


def do_update(event): 
    w = event.widget 
    number = float(qedit.get()) 
    w['text'] = '{}'.format(number) 

# The following settings can only be done after both the 
# widgets and callbacks have been created. 
vcmd = root.register(is_number) 
qedit['validate'] = 'key' 
qedit['validatecommand'] = (vcmd, '%P') 
result.bind('<<UpdateNeeded>>', do_update) 

# Run the event loop. 
root.mainloop()