Error - Default argument is mutable

[jacklong]

import doctest

def foo(bar=[]):
"""Error: Default argument is mutable.

Default argument values are evaluated only once at function definition time,
which means that modifying the default value of the argument will affect
all subsequent calls of the function.

>>> foo()
['baz']
>>> foo()
['baz', 'baz']
>>> foo()
['baz', 'baz', 'baz']
"""
bar.append("baz")
print bar

doctest.testmod()

[jacklong]

代码粘贴进来空格没了，如何缩进？

[tkliuxing]

@jacklong 在这里贴代码一般用gist
还有,你的主题要表达什么呢?

[dddd]

默认参数值是可变对象

可以这样:
def foo(bar=None):
if bar is None:
bar = []

看这里……
http://effbot.org/zone/default-values.htm

[dant]

默认参数指向的对象在定义函数的时候就创建了