class Test:
	def __init__(self, x=[]):
		self.x = x

a = Test()
b = Test()

a.x.append(1)

print(a == b)		# False

# Suprised... Why would this be equal?
print(a.x == b.x)	# True

class Test_Isolation:
	def __init__(self, x=None):
		if x is None:
			self.x = []
		else:
			self.x = x

a = Test_Isolation()
b = Test_Isolation()

a.x.append(1)

# Expected
print(a.x == b.x)	# False