Python Can'；t覆盖标签Tkinter

get_recs

由

start

按钮触发。

get_recs

中的循环尝试首先删除任何现有标签（但总是失败），然后创建标签，写入标签，然后将其添加到网格中。但是，每次按下

start

，现有标签不会被销毁，新标签不会被替换，而是被创建。我只能假设这意味着每次执行循环时，它都会创建单独的标签，这可以解释为什么它们从未被销毁，但我不明白为什么。代码如下：

import pandas as pd
import numpy as np
from tkinter import *
from tkinter.filedialog import askopenfilename
from tkinter.messagebox import showwarning, showinfo

movies = pd.read_csv('C:/Users/Admin/Python Programs/ml-latest-small/movies.csv')
ratings = pd.read_csv('C:/Users/Admin/Python Programs/ml-latest-small/ratings.csv')

ratings.drop(['timestamp'], axis=1, inplace= True)  

class App(Frame):

    def replace_name(x):
      return movies[movies['movieId']==x].title.values[0]

    ratings.movieId = ratings.movieId.map(replace_name)

    M = ratings.pivot_table(index=['userId'], columns=['movieId'], values='rating')

    def pearsons(s1, s2):
        s1_c = s1 - s1.mean()
        s2_c = s2 - s2.mean()
        return np.sum(s1_c * s2_c) / np.sqrt(np.sum(s1_c ** 2) * np.sum(s2_c ** 2))

    def get_recs(self):
        movie_name = self.mn.get()
        num_recs_str = self.nr.get()
        num_recs = int(num_recs_str)
        reviews = []
        for title in App.M.columns:
            if title==movie_name:
                continue
            cor = App.pearsons(App.M[movie_name], App.M[title])
            if np.isnan(cor):
                continue
            else:
                reviews.append((title, cor))

        reviews.sort(key=lambda tup: tup[1], reverse=True)
        Frame3= Frame(root, bg= 'red')
        Frame3.grid()
        #for i in range(num_recs):
            #exec("Label%d=Label(Frame3,text='', fg = 'blue')\nLabel%d.grid()" % (i,i))
        #var_exists = 'Label0' in locals() or 'Label0' in globals()

        for i in range(num_recs):
            try:
                exec("Label%d.destroy()" % (i))
            except (NameError):
                pass

            exec("Label%d=Label(Frame3,text='', fg = 'blue')\n" % (i))
            exec("Label%d.config(text=%s)" % (i,reviews[i]))
            exec("Label%d.grid()" % (i))
            print ("success")

            #exec("print (%d)" % (i))
        #for x in reviews:
            #self.label3.config(text= "\n" + str(reviews[:num_recs]))
        #self.label3.config(text=reviews[:num_recs])
        return reviews[:num_recs]

    def __init__(self, master):

        Frame.__init__(self, master)
        Frame1 = Frame(master)
        Frame1.grid()
        Frame2 = Frame(master)
        Frame2.grid()
        self.filename = None
        label1=Label(Frame1, text="Movie: ").grid(row=0, sticky=W)
        label2=Label(Frame1, text="Recommendations: ").grid(row=1, sticky=W)
        #self.label3=Label(master, text = "", font = 'Purisa', fg='blue')
        #self.label3.grid(row = 3)
        self.mn = Entry(Frame1)
        self.mn.grid(row = 0, column = 1, sticky=W)
        #self.mn.delete(0, END)
        self.mn.insert(0, "Enter Movie Name")
        self.nr = Entry(Frame1)
        self.nr.grid(row = 1, column = 1, sticky=W)
        #self.nr.delete(0, END)
        self.nr.insert(0, "Enter Number of Recommendations")
        button1 = Button(Frame2, text="Start", command=self.get_recs)
        button2 = Button(Frame2, text="Exit", command=master.destroy)
        button1.grid(row = 0, column = 0, padx= 5, pady = 5, sticky =W)
        button2.grid(row = 0, column = 1, padx = 5, pady =5, sticky =W)
        self.grid()

root = Tk()
root.title("Recommender")
root.geometry("500x500")
app = App(root)
root.mainloop()

---

您的代码抛出一个NameError，因为您的标签是在本地创建的。在第二次单击时，您无法接触到它们，并且由于您只是

pass

ing in except block，所以您什么也看不到

一种方法是，可以将标签创建为类变量

for i in range(num_recs):
    try:
        exec("self.Label%d.destroy()" % (i))

    except NameError:
        print("A NameError has occured")

    except AttributeError:
        exec("self.Label%d=Label(Frame3,text='', fg = 'blue')\n" % (i))
        exec("self.Label%d.config(text=%s)" % (i,reviews[i]))
        exec("self.Label%d.grid()" % (i))

代替这种方法，您可以将所有标签放入列表中，然后检查所述标签是否在列表中。这是一个更好的方法

#a list created in global scope to store all labels
labels = []

def get_recs(self):
    ....
    for i in range(num_recs):
        try:
            for label in labels:
                if label["text"] == reviews[i]:
                    label.destroy() #destroy the matching label
                    labels.remove(label) #remove it from labels list
        except (NameError):
            #Please don't just pass Exceptions. They are there for a reason
            print("A NameError has occured") 

        labels.append(Label(Frame3,text='', fg = 'blue'))
        labels[-1].config(text=reviews[i])
        labels[-1].grid()

---

不要使用exec！！这可能很方便，但不要这样做。对于在该循环中创建的每个标签，基本上都会有一个NameError，但您不会知道，因为您传递了它