内置类属性__doc__在Python中做什么？
所有函数都具有内置属性__doc__，该属性返回函数源代码中定义的doc字符串。
def foo():
""" This is an example of how a doc_string looks like.
This string gives useful information about the function being defined.
"""
pass
print foo.__doc__让我们看看打印时的样子
This is an example of how a doc_string looks like.
This string gives useful information about the function being defined.