On Fri, 17 Feb 2012 16:53:00 +0900, Zheng Li wrote:
> def method1(a = None):
> print a
>
> i can call it by
> method1(*(), **{'a' : 1})
>
> I am just curious why it works and how it works?
> and what do *() and **{'a' : 1} mean?
In a function call, an argument consisting of * followed by an expression
of tuple type inserts the tuple's elements as individual positional
arguments. An argument consisting of ** followed by an expression of
dictionary type inserts the dictionary's elements as individual keyword
arguments.
So if you have:
a = (1,2,3)
b = {'a': 1, 'b': 2, 'c': 3}
then:
func(*a, **b)
is equivalent to:
func(1, 2, 3, a = 1, b = 2, c = 3)
> when I type *() in python shell, error below happens
>
> File "<stdin>", line 1
> *()
> ^
> SyntaxError: invalid syntax
The syntax described above is only valid within function calls.
There is a similar syntax for function declarations which does the reverse:
> def func(*a, **b):
print a
print b
> func(1, 2, 3, a = 1, b = 2, c = 3)
(1, 2, 3)
{'a': 1, 'c': 3, 'b': 2}
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