New Instance gets Keyword parameter from previous instance in Python

Question

I have a question regarding new instances in Python. The following code as a minimal example

class A(object):
    def __new__(cls, *p, **k):
        inst = object.__new__(cls)
        return inst

    def __init__(self, params=[]):
        self.params = params

    def add_param(self, p):
        self.params.append(p)


a = A()
print a.params
a.add_param(1)
a.add_param(2)
print a.params


b = A()
print b.params

With output

[]
[1, 3]
[1, 3]

From my basic understanding I would have suspected, that b would also have an empty parameter list. However, b is created with the parameters added to a.

So, my question is: Why is that and how can I get to instantiate b without any parameters (apart from explicitly providing params=[] as an argument).