python参数调用

下面是文档给出的（python v2.7.3  5.3.4 Calls）

call                 ::=  primary "(" [argument_list [","]
                          | expression genexpr_for] ")"
argument_list        ::=  positional_arguments ["," keyword_arguments]
                            ["," "*" expression] ["," keyword_arguments]
                            ["," "**" expression]
                          | keyword_arguments ["," "*" expression]
                            ["," "**" expression]
                          | "*" expression ["," "*" expression] ["," "**" expression]
                          | "**" expression
positional_arguments ::=  expression ("," expression)*
keyword_arguments    ::=  keyword_item ("," keyword_item)*
keyword_item         ::=  identifier "=" expression

 相关摘要：

http://blog.csdn.net/qinyilang/article/details/5484415

上面一篇博客有说到：

参数的次序定义，不用的可以跳过：

1）必须的参数
2）可选的参数
3）过量的位置参数
4）过量的关键字参数

 

不只在定义时这样，在使用函数时也必须这样。

>>> def say(msg, times = 1):
    print msg*times

    
>>> say("hello")
hello
>>> say("hello",5)
hellohellohellohellohello
>>> say(times = 3, msg="abc")
abcabcabc
>>> say(msg="abcd", times = 4)
abcdabcdabcdabcd
>>> say("a", times = 5)
aaaaa
>>> say(msg = "a", 5)
SyntaxError: non-keyword arg after keyword arg

调用时也不可以在关键字参数后面使用非关键字参数。