RuntimeError: dictionary changed size during iteration,可变参数，关键字参数

>>> a={'x':1,'xx':2}

>>> for i in a:
if i=='x':
a[i]=6

>>> a
{'x': 6, 'xx': 2, 'xxx': 33}

>>> for i in a:
if i=='x':
a[i]=3
a['xxx']=33

Traceback (most recent call last):
  File "<pyshell#26>", line 1, in <module>
    for i in a:
RuntimeError: dictionary changed size during iteration

对于数据字典，如果遍历过程中对于key添加或者删除，即key的size发送改变，会报错。RuntimeError: dictionary changed size during iteration

Solve：

遍历数据字典的keys()

>>> for i in ():
if i=='x':
a[i]=3
a['xxx']=33



>>> a
{'x': 3, 'xx': 2, 'xxx': 33}

可变参数：

参数是tuple

>>> def test(*num):
print type(num)



>>> test(1)
<type 'tuple'>
>>> test(3)
<type 'tuple'>
>>> test(1,2)
<type 'tuple'>

关键字参数：

关键字参数是字典

>>> def test(**num):
for i in ():
print i



>>> test(city='bj',name=24)
city
name

>>> def test(**num):
print num
>>> test(a)
Traceback (most recent call last):
  File "<pyshell#43>", line 1, in <module>
    test(a)
TypeError: test() takes exactly 0 arguments (1 given)
>>> test('a'='5')
SyntaxError: keyword can't be an expression
>>> test(a='5')
{'a': '5'}