Python default value in constractor is ignored?

Question

I'm new to python. When I code in Python I notice this strange behavior:

Class x:

class x:
    x1 = 0

    def __init__(self, x):
        self.x1 = x

Class xcontainer:

class xContainer:
    coint = []

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

    def add_x(self, x):
        self.coint.append(x)

when I try to run this code:

def Main():
    list_xcon = []
    for i in range (0,2):
        xcon = xContainer()
        for j in range (i, i+1):
            xcon.add_x(x(j))
        list_xcon.append(xcon)

    for xcont in list_xcon:
        for xc in xcont.coint:
            print xc.x1

I get those results:

0 1 0 1

but when I run this code:

def Main():
    list_xcon = []
    for i in range (0,2):
        listt = []
        xcon = xContainer(listt)
        for j in range (i, i+1):
            xcon.add_x(x(j))
        list_xcon.append(xcon)

    for xcont in list_xcon:
        for xc in xcont.coint:
            print xc.x1

I get those results:

0 1

Why is that? According to class xcontainer, the default of coint should be [] - empty list. So why sending empty list change the result?

By the way, I read that using coint = None as default and checking if coint is None: coint = [] is better way, but it seems that it does not change the results here.

I will appreciate any explanation. I'm confused.

Thanks.