仅限位置参数(/)

# Python 3.8 新增
def demo1(a,b,/):
    return a,b

if __name__ == '__main__':
    demo1(1,2) # right
    demo1(1,b=2) # error


# demo1(1,b=2) 报错：
'''
Traceback (most recent call last):
  File "E:\PyProject\pytestDemo\demo10.py", line 19, in <module>
    demo1(1,b=2) # error
TypeError: demo1() got some positional-only arguments passed as keyword arguments: 'b'
'''

仅限关键字参数(*)

# Python3 新增
def demo2(a,*,b,c):
    return a,b,c

if __name__ == '__main__':
    demo2(1,b=2,c=3) # right
    demo2(1,2,3)  # error

# demo2(1,2,3) 报错： 
'''
Traceback (most recent call last):
  File "E:\PyProject\pytestDemo\demo10.py", line 18, in <module>
    demo2(1,2,3)
TypeError: demo2() takes 1 positional argument but 3 were given
'''