当在Tkinter中打开新窗口时出现错误信息

Question

我是Tkinter的初学者，我想了解如何打开一个新窗口来计算某些变量。

在这个例子中，出现一个带有按钮的第一个窗口（“输入”）。按“开始”后，创建一个新的窗口，我可以导入一个圆周值，按直径按钮“转换”转换。

当我按下这个BUTTOM出现在控制台中的错误：

Exception in Tkinter callback 
Traceback (most recent call last): 
    File "C:\Python27\lib\lib-tk\Tkinter.py", line 1470, in __call__ 
    return self.func(*args) 
    File "C:/Users/samsung/PycharmProjects/test_FirstDensity/openANDread.py", line 55, in convert 
    convert = tk.Button(c2d, text="Convert", command=convert_c2d, activeforeground="red") 
UnboundLocalError: local variable 'convert_c2d' referenced before assignment 

我尝试了几种解决方案，而解决我的问题。

我的代码是：

from __future__ import division 
from Tkinter import * 
from math import pi 
import tkMessageBox 
import Tkinter, Tkconstants, tkFileDialog 
from numpy import nan 
import Tkinter as tk 




class MainWindow(Frame): 
    def __init__(self): 
     Frame.__init__(self) 
     self.filename = None 
     self.master.title("input") 
     self.master.minsize(250, 150) 
     self.grid(sticky=E+W+N+S) 

     top=self.winfo_toplevel() 
     top.rowconfigure(0, weight=1) 
     top.columnconfigure(0, weight=1) 

     for i in range(1): self.rowconfigure(i, weight=1) 
     self.columnconfigure(1, weight=1) 

     self.button0 = Button(self, text="start", command=self.convert, activeforeground="red") 
     self.button0.grid(row=0, column=1, pady=2, padx=2, sticky=E+W+N+S) 

    def convert(self): 
     c2d = Tk() 
     c2d.title("C2DBH converter") 
     c2d.minsize(350, 150) 
     c2d.grid() 

     res = StringVar(c2d) 
     res.set("---") 


     for i in range(3): c2d.rowconfigure(i, weight=1) 
     c2d.columnconfigure(1, weight=1) 

     label_c = tk.Label(c2d, text='Circumference') 
     label_c.grid(row=0, column=0, padx=2, sticky=E+W+N+S) 

     entry_c = Entry(c2d) 
     entry_c.grid(row=0, column=1, padx=2,sticky=E+W+N+S) 

     label_d = tk.Label(c2d, text='Diameter') 
     label_d.grid(row=1, column=0, padx=2, sticky=E+W+N+S) 

     result = tk.Label(c2d, textvariable=res, fg="red") 
     result.grid(row=1, column=1, pady=2, padx=2, sticky=E+W+N+S) 

     convert = tk.Button(c2d, text="Convert", command=convert_c2d, activeforeground="red") 
     convert.grid(row=2, column=0, columnspan=2, pady=2, padx=2, sticky=E+W+N+S) 

     def convert_c2d(n): 
      if not n.get(): 
       return res.set("Insert a numeric value.") 
      try: 
       c = float(n.get()) 
       diameter = c/pi 
       return res.set(str(diameter)) 
      except ValueError: 
       return res.set("Insert a numeric value.") 

Answer 1

你应该定义函数就引用它之前。

>>> def f(): 
...  convert_c2d(1) 
...  def convert_c2d(n): 
...   pass 
... 
>>> f() 
Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "<stdin>", line 2, in f 
UnboundLocalError: local variable 'convert_c2d' referenced before assignment 
>>> def g(): 
...  def convert_c2d(n): 
...   pass 
...  convert_c2d(1) 
... 
>>> g() 
>>> 

---

如下代码的简单变化将解决你的问题：

def convert_c2d(n): 
    if not n.get(): 
     return res.set("Insert a numeric value.") 
    try: 
     c = float(n.get()) 
     diameter = c/pi 
     return res.set(str(diameter)) 
    except ValueError: 
     return res.set("Insert a numeric value.") 

convert = tk.Button(c2d, text="Convert", command=convert_c2d, activeforeground="red") 
convert.grid(row=2, column=0, columnspan=2, pady=2, padx=2, sticky=E+W+N+S) 

UPDATE

convert_c2d需要的参数。但tkinter不会用参数调用命令回调。你应该使用其他功能（或下面拉姆达）传递：

convert = tk.Button(c2d, text="Convert", command=lambda: convert_c2d(entry_c), 
        activeforeground="red") 

，或者你可以改变convert_c2d不采取任何参数，并进行功能直接访问entry_c。 （嵌套函数可以从封闭范围访问变量）。