如何使用 Python 中的 Tkinter 使按钮仅单击一次？

Question

So I made a sill calculator that just takes an input of 'banana' and 'milk' when the user does such calculation: banana + milk, then it returns 'banana milk' and so on. Since these strings are not a number, I want the buttons to be only clickable once so that it will never be 'banana banana + milk' but only 'banana + milk' or 'milk + banana'...

Also, whenever the user puts only one input such as 'banana' and press Enter (finalPress), I want to print out only 'banana', but with my code, it goes to elif phrase[0] == 'Banana': and prints out 'banana milk' even though I only press 'banana'. How can I fix this issue?

Below is my code:

from tkinter import *

phrase = []
phrase_string = ''


# To press any button
def press(item):
    global phrase, phrase_string
    if item == 'Banana':
        phrase.append('Banana')
    elif item == 'Milk':
        phrase.append('Milk')
    elif item == 'AND':
        phrase.append(' and ')

    phrase_string = ''
    for ele in phrase:
        phrase_string += ele
    return equation.set(phrase_string)


# This is enter
def finalPress():
    global phrase, phrase_string
    if phrase[0] in ['Banana', 'Milk'] and len(phrase) is 1:
        phrase = phrase[0]
    elif phrase[0] == 'Banana':
        if phrase[1] == ' and ':
            phrase.clear()
            phrase = 'Banana Milk'
    elif phrase[0] == 'Milk':
        if phrase[1] == ' and ':
            phrase.clear()
            phrase = 'Milk Banana'

    return equation.set(phrase)


# Clear the content
def clearContent():
    pass


# Driver code
if __name__ == '__main__':
    # create application window
    app = Tk()

    # title
    app.title("Slly Calculator")

    # geometry
    app.geometry('290x162')

    # background color
    app.configure(bg='pink')

    equation = StringVar()
    windows = Entry(app, textvariable=equation)
    windows.grid(columnspan=5, ipadx=100, ipady=10)
    equation.set('Press Buttons Please')

    # Create buttons and other accessories
    button1 = Button(app, text=' Banana ', fg='yellow', bg='purple',
                     command=lambda: press('Banana'), height=2, width=10)
    button1.grid(row=2, column=0, sticky="NSEW")

    button2 = Button(app, text=' Milk ', fg='brown', bg='pink',
                     command=lambda: press('Milk'), height=2, width=10)
    button2.grid(row=2, column=1, sticky="NSEW")

    plus = Button(app, text='AND', fg='black', bg='white',
                  command=lambda: press('AND'), height=2, width=10)
    plus.grid(row=4, column=0, sticky="NSEW")

    equal = Button(app, text='ENTER', fg='black', bg='white',
                   command=finalPress, height=2, width=10)
    equal.grid(row=4, column=2, sticky="NSEW")

# start the GUI
app.mainloop()

Thank you so much: :-D

Answer 1

I didn't take a look on function of "enter" button, because I'm not really sure, what it's suppose to do. I changed only this:

from tkinter import *

phrase = []
phrase_string = ''
words_product = ['Banana', 'Milk']
words_conjunction = [" and "]


# To press any button
def press(item):
    global phrase, phrase_string

    # len(phrase) != 0 - don't allow to write 'and' when nothing was pressed before to avoid i.e. 'and banana milk'
    # item not in phrase - to avoid writing product more then one time to avoid banana and milkmilk or bananabanana

    if item in words_product:
        if all([item not in phrase]):
            phrase.append(item)
    elif item in words_conjunction:
        if all([len(phrase) != 0, item not in phrase]):   # if you want want allow to banana and milk and something
            phrase.append(item)                           # delete ' item not in phrase"

    phrase_string = ''

    for ele in phrase:
        phrase_string += ele
    return equation.set(phrase_string)

And this:

plus = Button(app, text='AND', fg='black', bg='white',
              command=lambda: press(" and "), height=2, width=10)

So the full code is:

from tkinter import *

phrase = []
phrase_string = ''
words_product = ['Banana', 'Milk']
words_conjunction = [" and "]


# To press any button
def press(item):
    global phrase, phrase_string

    # len(phrase) != 0 - don't allow to write 'and' when nothing was pressed before to avoid i.e. 'and banana milk'
    # item not in phrase - to avoid writing product more then one time to avoid banana and milkmilk or bananabanana

    if item in words_product:
        if all([item not in phrase]):
            phrase.append(item)
    elif item in words_conjunction:
        if all([len(phrase) != 0, item not in phrase]):   # if you want want allow to banana and milk and something
            phrase.append(item)                           # delete ' item not in phrase"

    phrase_string = ''

    for ele in phrase:
        phrase_string += ele
    return equation.set(phrase_string)


# This is enter
def finalPress():
    global phrase, phrase_string
    if phrase[0] in ['Banana', 'Milk'] and len(phrase) == 1:
        phrase_string = phrase[0]
    elif phrase[0] == 'Banana' and phrase[1] == " and ":
        phrase.clear()
        phrase = 'Banana Milk'

    elif phrase[0] == 'Milk' and phrase[1] == " and ":
        phrase.clear()
        phrase = 'Milk Banana'

    return equation.set(phrase)


# Clear the content
def clearContent():
    pass


# Driver code
if __name__ == '__main__':
    # create application window
    app = Tk()

    # title
    app.title("Slly Calculator")

    # geometry
    app.geometry('290x162')

    # background color
    app.configure(bg='pink')

    equation = StringVar()
    windows = Entry(app, textvariable=equation)
    windows.grid(columnspan=5, ipadx=100, ipady=10)
    equation.set('Press Buttons Please')

    # Create buttons and other accessories
    button1 = Button(app, text=' Banana ', fg='yellow', bg='purple',
                     command=lambda: press('Banana'), height=2, width=10)
    button1.grid(row=2, column=0, sticky="NSEW")

    button2 = Button(app, text=' Milk ', fg='brown', bg='pink',
                     command=lambda: press('Milk'), height=2, width=10)
    button2.grid(row=2, column=1, sticky="NSEW")

    plus = Button(app, text='AND', fg='black', bg='white',
                  command=lambda: press(" and "), height=2, width=10)
    plus.grid(row=4, column=0, sticky="NSEW")

    equal = Button(app, text='ENTER', fg='black', bg='white',
                   command=finalPress, height=2, width=10)
    equal.grid(row=4, column=2, sticky="NSEW")

    # start the GUI
    app.mainloop()

I decided it's a good idea to make two lists. One words_product and the second one words_conjuction. First list only contains items like 'Banana', 'Milk' and here you will add all the products you will make buttons for. The second list is words_conjuction which contains only products separators like 'and', 'or' and whatever you are going to add in the future. With separating items on two mentioned groups (lists), it's easier to write code which will validate your input and to maintain the code in the future when you will add more words. And the main reason is: these two groups will definitely have different "validation rules".

For example:

if all([item not in phrase]):
            phrase.append(item)

Line phrase.append(item) will be only executed if all elements in list in all([item not in phrase]) will be True. In this case: if currently there is no 'item' in list phrase, add 'item' to the phrase list.

If you want to add your own validation rule you can just add something to the list:

if all([item not in phrase, len(phrase) > 2]):
                phrase.append(item)

It will add the item to the phrase list only when item is not currently in the phrase list and if phrase list length is greater then 2.

And also, as suggested before, there is possibility of making buttons normal/disabled (clickable/not clickable) but to be honest I'm not sure which way is better in this case. It depends how your program will finally look and what product/separators you are going to add. But here is the way you can change the button state:

button_name.config(state='normal')
button_name.config(state='disabled')

Example of using button state:

If you want to prevent user from pressing "add" button more then one time in a row, then you can just disable the "add" button after it's pressed and enable when user will press one of the product buttons.

Simplified program example to show you how it works:

from tkinter import *

phrase = []
outputstring = 'Press some buttons'
products = ['Banana', 'Milk']


def press(item):
    if item in products:
        button_1.config(state='disabled')
        button_2.config(state='disabled')
        button_and.config(state='normal')
    else:
        button_1.config(state='normal')
        button_2.config(state='normal')
        button_and.config(state='disabled')

    phrase.append(item)

    phrase_string = ''
    for ele in phrase:
        phrase_string += ele

    return output.config(text=phrase)


app = Tk()
app.title("Slly Calculator")
app.geometry('350x200')
app.configure(bg='pink')

# widgets
output = Label(app, text=outputstring, width='50')
button_1 = Button(app, text=' Banana ', fg='yellow', bg='purple', command=lambda: press('Banana'), height=2, width=10)
button_2 = Button(app, text=' Milk ', fg='brown', bg='pink', command=lambda: press('Milk'), height=2, width=10)
button_and = Button(app, text='AND', fg='black', bg='white', command=lambda: press("and"), height=2, width=10)

# grid
output.grid(row=0, column=0, columnspan='3', pady='10')
button_1.grid(row=2, column=0, sticky="NSEW")
button_2.grid(row=2, column=1, sticky="NSEW")
button_and.grid(row=4, column=0, sticky="NSEW")


app.mainloop()

If you want to disactivate a button when program starts (for example "and" to prevent user from writing something like "and Banana and Milk")

Change:

button_and = Button(app, text='AND', fg='black', bg='white', command=lambda: press("and"), height=2, width=10) 

to:

button_and = Button(app, text='AND', fg='black', bg='white', command=lambda: press("and"), height=2, width=10, state='disabled')

I hope you understand it better now:)