如何只询问用户一次的符号值而不是每次迭代？

Question

在当前状态下，此代码有效。它旨在成为音乐家的换位工具。我无法弄清楚如何只询问用户一次'符号'值，而不是每次成功迭代后。

import time
import sys
usr_list = ['A','BB','B','C','C#','D','EB','E','F','F#','G','AB']
u_list = []
t_list = []




def f():
    usr = int(input('Enter how many chords need to be transposed: '))
    while usr!=0:
        chord = input('\nEnter the chord that needs to be transposed: ').upper()
        if chord not in usr_list:
            print('Invalid Input')
        elif u_list.count(chord) >=1:
            print('Already typed')
        else:
            usr =usr-1
            u_list.append(chord)
            print('Chords that need to be transposed are:',u_list)
    while len(u_list)>0:
        chord = (u_list[0])
        sign = input('''1.Positive Transposition(+)
2.Negative Transpostion(-)

Your choice: ''')
        if sign == '1' or '+':
            sign = '+'
            time.sleep(0.2)
            print('\nPositive shift initiating')
            time.sleep(0.5)
            t_key = int(input('Enter value of transposition: '))
            chord_value = int(usr_list.index(chord))
            chord_transpose = chord_value + t_key
            if chord_transpose >= 12:
                chord_transpose = chord_transpose - 12
                print(usr_list[chord_transpose])
            elif chord_transpose < 12:
                del u_list[0]
                t_list.append(usr_list[chord_transpose])
                print(u_list)
            else:
                print('Invalid Input, Try Again!') 
        elif sign == '2' or '-':
            sign = '-'
            time.sleep(0.2)
            print('\nNegative initiating')
            time.sleep(0.5)
            t_key = int(input('Enter value of transposition: '))
            chord_value = int(usr_list.index(chord))
            chord_transpose = chord_value - t_key
            if chord_transpose >= 12:
                chord_transpose = chord_transpose + 12
                print(usr_list[chord_transpose])
            elif chord_transpose < 12:
                del u_list[0]
                t_list.append(usr_list[chord_transpose])
                print(u_list)
            else:
                print('Invalid')
        else:
            print('Invalid')
        print(t_list)
f()

目前它向用户询问他们想要输入的多个和弦，然后逐个使用列表对它们进行转置。在询问符号值时，我不知道如何仅询问该值一次。

Answer 1

现在，分配sign的输入语句位于while循环中。如果您希望仅提示用户一次，则需要将输入语句放在while循环之前或之间。