大家去试试这个，有意思

def func(b,a = []):
	if b:
		a = b
	return a

b = [3]
print(func(b),func(None))
# 结果：([3], [])

def func2(b,a = []):
	if b:
		a.append(b)
	return a

b = 3
print(func2(b),func2(None))
# 结果：([3], [3])