wacky python bug

gistfile1.py

class SomeClass:
    def __init__(self, some_var=[]):
        self.data = some_var
    def append(self, var):
        self.data.append(var)

a = SomeClass()
a.append(1)
a.append(2)

print a.data
# [1, 2]

b = SomeClass()
print b.data
# [1, 2]

# freaky, huh?