Python: why did the y.append(x) value of object a become the argument for object c?

Question

def test(x,y=[]):
print("======================")
print("x = "+ str(x))
print("y = "+ str(y))
y.append(x)
print("y.append(x) = "+ str(y))
return y

a=test(111)
print("a = "+ str(a))
b=test(2, []) # TWO arguments...
print("b = "+ str(b)) # outputs b = [2] --> does this list have a 'none' or something?
c=test(3)
print("c = "+ str(c)) # how come the value 111 is suddenly passed to parameter y=[]?

Why did the y.append(x) value of object a become the argument/parameter for object c?

Answer 1

Function 'test' uses a cached `list` object when it is called without specifying an argument for parameter <y>. So the `list` object that is returned on the first and third call are the same one.

Try to check their IDs and you'll see they both refer to the same `list` object 👇

print(id(a), id(c))

Answer 2

can you paste your outputs