我想把操作符作为一个列表，然后从列表中调用一个元素作为操作符。在
如果我没有在运算符周围加引号，那么列表中逗号的语法错误：File "p22.py", line 24
cat = [+,-,*]
^
SyntaxError: invalid syntax
如果我把引语放在周围，那么我似乎失去了运算符的功能，如本例所示：
^{pr2}$
以下是完整代码：import random
def start():
print('\n________________________________________')
print('| |')
print('| Zach\'s Tutorifier! |')
print('| |')
print('| |')
print('| Instructions: |')
print('| Select the type of math you want |')
print('| to practice with: |')
print('| 1-Add 2-Subtract 3-Multiply |')
print('|--------------------------------------|')
start()
math = int(input('> ')) - 1
cat = ['+','-','*']
def problems():
which = cat[math]
x = random.randint(0,9)
y = random.randint(0,9)
a = (x which y)
print('What is %i %s %i?' % (x, which, y) )
answer = input('> ')
if answer == a:
print('Congratulations! Try again? (Y/N)')
again = input('> ')
if again == 'Y' or again == 'y':
problems()
else:
start()
else:
print('Try again!')
problems()
