使用 Tkinter 显示条目文本时出现问题

Question

我是python的新手。我正在尝试编写一个程序来参考哈佛和 APA 风格的书籍、书籍章节和期刊文章。我需要能够打印来自用户的条目。

代码显示三个窗口。首先，要求用户选择参考风格（哈佛/APA），当点击按钮时，它会打开第二个窗口，允许用户选择来源（书籍/书籍章节/期刊）。然后打开第三个窗口，允许用户输入所需的信息（作者/年份/标题等）。

在此之后，用户必须单击另一个按钮完成才能看到完整的参考。要可视化执行，请选择哈佛，然后选择 Book，因为我只编写了那部分代码。

from tkinter import *

def book_harvard():
    reference = author_entry.get()
    reference_1 = year_entry.get()
    reference_2 = title_entry.get()
    string_to_display = reference + reference_1 + reference_2
    print(string_to_display)


def TypeofTextHarvard():
    second = Toplevel(first)
    first.withdraw()
    second.title("Type of Source")
    Source = Label (second, text = "What type of source would you like to reference?").grid(column = 1, row = 0)
    Book = Button (second, text = "Book", command = Harvard).grid(column = 1, row = 1)
    Chapter = Button (second, text = "Book Chapter").grid (column = 1, row = 2)
    Journal = Button (second, text = "Journal Article").grid (column = 1, row = 3)

first = Tk()
first.title("Referencing Style")
Reference = Label (first, text = "Which referencing style would you like to use?").grid(column = 1, row = 0)
Harvard = Button (first, text = "Harvard Style", command = TypeofTextHarvard).grid (column = 1, row = 1)
APA = Button (first, text = "APA Style").grid (column = 1, row = 2)


def Harvard():
    third = Toplevel()
    third.title("book")
    author = StringVar()
    year = StringVar()
    title = StringVar()

    author_label = Label(third, text = "Author")
    author_entry = Entry(third)
    year_label = Label(third, text = "Year")
    year_entry = Entry(third)
    title_label = Label(third, text = "Title")
    title_entry = Entry(third)
    button_1 = Button(third, text = "Done", command = book_harvard)
    author_label_2 = Label(third, textvariable = author)
    year_label_2 = Label(third, textvariable = year)
    title_label_2 = Label(third, textvariable = title)

    author_label.grid (row = 0, column = 0)
    author_entry.grid (row = 0, column = 1)
    year_label.grid (row = 1, column = 0)
    year_entry.grid (row = 1, column = 1)
    title_label.grid (row = 2, column = 0)
    title_entry.grid (row = 2, column = 1)
    button_1.grid (row = 3, column = 0)
    author_label_2.grid (row = 4, column = 1)
    year_label_2.grid (row = 4, column = 2)
    title_label_2.grid (row = 4, column = 3)


first.mainloop()

但是我得到以下错误：

reference = author_entry.get()
NameError: name 'author_entry' is not defined

Answer 1

NameError 的原因是因为author_entry 是Harvard() 函数的局部变量，所以不能在它之外引用，例如在单独的book_harvard() 函数中。最简单（尽管不是最好）的解决方案是将其设为全局变量。其他的Entry 小部件可能有同样的问题，所以在下面的代码中我已经声明了所有的global。

我还注意到您可能遇到的另一个潜在问题，即将grid() 方法的返回值分配给一个变量。例如：

Book = Button(second, text="Book", command=Harvard).grid(column=1, row=1)

这不是你想的那样，因为grid() 方法总是返回None，所以这是分配给Book 的值。我还没有修复这些，但这样做很容易，只需先创建小部件并将其分配给一个变量，然后在另一行，全部为variable.grid(...)。

最后一条建议：阅读并开始关注PEP 8 - Style Guide for Python Code。我已经在某种程度上对您的代码版本进行了此操作，其中的修复如下所示。

仅供参考：问题Best way to structure a tkinter application 的公认答案描述了一种极好的面向对象的方式来构建和实现基于 Tkinter 的应用程序。

from tkinter import *


def book_harvard():
    global author_entry, year_entry, title_entry  # ADDED

    reference = author_entry.get()
    reference_1 = year_entry.get()
    reference_2 = title_entry.get()
    string_to_display = reference + reference_1 + reference_2
    print(string_to_display)


def TypeofTextHarvard():
    second = Toplevel(first)
    first.withdraw()
    second.title("Type of Source")
    Source = Label(second, text = "What type of source would you like to reference?").grid(column=1, row=0)
    Book = Button(second, text="Book", command=Harvard).grid(column=1, row=1)
    Chapter = Button(second, text="Book Chapter").grid(column=1, row=2)
    Journal = Button(second, text="Journal Article").grid(column=1, row=3)


first = Tk()
first.title("Referencing Style")
Reference = Label(first, text="Which referencing style would you like to use?").grid(column=1, row=0)
Harvard = Button(first, text="Harvard Style", command=TypeofTextHarvard).grid(column=1, row=1)
APA = Button(first, text="APA Style").grid(column=1, row=2)


def Harvard():
    global author_entry, year_entry, title_entry  # ADDED

    third = Toplevel()
    third.title("book")
    author = StringVar()
    year = StringVar()
    title = StringVar()

    author_label = Label(third, text="Author")
    author_entry = Entry(third)
    year_label = Label(third, text="Year")
    year_entry = Entry(third)
    title_label = Label(third, text="Title")
    title_entry = Entry(third)
    button_1 = Button(third, text="Done", command=book_harvard)
    author_label_2 = Label(third, textvariable=author)
    year_label_2 = Label(third, textvariable=year)
    title_label_2 = Label(third, textvariable=title)

    author_label.grid(row=0, column=0)
    author_entry.grid(row=0, column=1)
    year_label.grid(row=1, column=0)
    year_entry.grid(row=1, column=1)
    title_label.grid(row=2, column=0)
    title_entry.grid(row=2, column=1)
    button_1.grid(row=3, column=0)
    author_label_2.grid(row=4, column=1)
    year_label_2.grid(row=4, column=2)
    title_label_2.grid(row=4, column=3)


first.mainloop()