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question about function pointer

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  question about function pointer Zheng Li <dllizheng@gmail.com> - 2012-02-17 16:53 +0900
    Re: question about function pointer Nobody <nobody@nowhere.com> - 2012-02-17 09:55 +0000
      Re: question about function pointer 88888 Dihedral <dihedral88888@googlemail.com> - 2012-02-17 05:20 -0800

#20539 — question about function pointer

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?

when I type *() in python shell, error below happens

  File "<stdin>", line 1
    *()
    ^
SyntaxError: invalid syntax

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#20543

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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#20553

在 2012年2月17日星期五UTC+8下午5时55分11秒，Nobody写道：
> 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}

In the functional programming view, 2 to 5
object parameters are enough to invoke a function.
 
But the tuple and dictionary packing and unpacking  
are not free in the run time.


Enhancement to operations of  basic types in Python can speed up everything.  

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