python类和函数中使用静态变量的方法

class foo:
def __init__(self, n=0):
self.n = n
def __call__(self, i):
self.n += i
return self.n
a=foo()
print a(1)
print a(2)
print a(3)
print a(4)

def foo2 (n=0):
class acc:
def __init__ (self, s):
self.s = s
def inc (self, i):
self.s += i
return self.s
return acc (n).inc
a=foo2()
print a(1)
print a(2)
print a(3)
print a(4)

def foo3 (i, L=[]):
if len(L)==0:
L.append(0)
L[0]+=i
return L[0]
 
print foo3(1)
print foo3(2)
print foo3(3)
print foo3(4)

1
3
6
10