python - 使用 tkinter 减少输入字母不起作用

Question

我程序中的数字输入小部件正常工作，最多只允许输入 3 个数字，而我试图在不同的输入小部件中做同样的事情，但对于字符，限制不起作用，我没有知道为什么。由于您使用的是字母，您是否必须以不同的方式使用它？

这是我的代码:

def only_letters_max_86(action, char):
if action == "1":
    # a character is inserted (deletion is 0) allow the insertion 
    # only if the inserted character char is a letter
    return char.isalpha() and len(char) <= 86
else:
    # allow deletion
    return True

def only_numbers_max_3(action, new_text):
if action == "1":
    return new_text.isdigit() and len(new_text) <= 3
else:
    return True


def main():

validate_letter = window.register(only_letters_max_86)
validate_nb = window.register(only_numbers_max_3)

label = Label(window, width = 30, background = 'lightgreen', text='enter temperature, only numbers')
label.grid(row=0, column=0)

entry_tempp = Entry(window, width = 30, validate="key", validatecommand=(validate_nb, '%d', '%P'))
entry_tempp.grid(row = 0, column = 1)

#create another label and entry object for location

label_numb = Label(window, width = 30, background = 'lightgreen', text='enter location, only letters')
label_numb.grid(row=1, column=0)

entry_locations = Entry(window, width = 30, validate="key", validatecommand=(validate_letter, '%d', '%S', '%v'))
entry_locations.grid(row = 1, column = 1)

Answer 1

这一行:entry_locations = Entry(window, width = 30, validate="key", validatecommand=(validate_letter, '%d', '%S', '%v'))

您正在将 '%S' 传递给您的 validate_letter 函数，查看文档意味着:

'%S': If the call was due to an insertion or deletion, this argument will be the text being inserted or deleted.

所以我的猜测是 only_letters_max_86(action, char) 中的 char 只获取正在插入的字符，该字符的长度始终为 1，导致您的检查失败。尝试将 %S 更改为 %P，这会为您提供:

'%P': The value that the text will have if the change is allowed.

文档链接:http://infohost.nmt.edu/tcc/help/pubs/tkinter/web/entry-validation.html