def foo(arg):
    arg = 2
    print(arg)

a = 1
foo(a)  # 输出：2
print(a) # 输出：1

def bar(args):
    args.append(1)

b = []
print(b)#　输出：[]
print(id(b)) # 输出：4324106952
bar(b)
print(b) ＃　输出：[1]
print(id(b))  # 输出：4324106952

def foo(x, a_list=[]):
    a_list.append(x)
    return a_list

print foo(‘one‘)  #[‘one‘]
print foo(‘one‘)  #[‘one‘, ‘one‘]