问python 方法参数中*代表什么？

class A(object):

    def foo1(self, a=None, *, b=False):
        print(a)
        print(b)
        print(1111)

    def foo2(self, a=None, b=False):
        print(a)
        print(b)
        print(1111)

a = A()
a.foo1(a='a', b='xxx')
a.foo2(a='a', b='xxx')