Asterisk sign in python

[sarmin]

Hi Pythoners...

It seems to me the Asterisk (*) sign in python means many things...

if a python code line looks like this:
def__init__(sel f, func, *param):
bla bla bla...

and then u have something like this:
func(*param)

and then something like this:
def Wrapper(select, func, param):
bla bla bla...

I took this section of code from the 'Python Cookbook' textbook page
223 about 'Running Functions in the future'...

I just cant figure out what is the asterisk (*) sign for and what is
the different between *param and param??

Many thanks Pythoners...

Regards
sarmin

[John Roth]

Re: Asterisk sign in python

"sarmin" <sarmin_kho@yah oo.com> wrote in message
news:mailman.15 9.1077796055.85 94.python-list@python.org ...[color=blue]
> Hi Pythoners...
>
> It seems to me the Asterisk (*) sign in python means many things...
>
> if a python code line looks like this:
> def__init__(sel f, func, *param):
> bla bla bla...
>
> and then u have something like this:
> func(*param)
>
> and then something like this:
> def Wrapper(select, func, param):
> bla bla bla...
>
> I took this section of code from the 'Python Cookbook' textbook page
> 223 about 'Running Functions in the future'...
>
> I just cant figure out what is the asterisk (*) sign for and what is
> the different between *param and param??
>
> Many thanks Pythoners...
>
> Regards
> sarmin[/color]

It's for variable length parameter lists. In a function
definition, one * is a list of additional positional
parameters, two **s is a dictionary of additional
keyword parameters.

In a function call, one * is a list of additional
positional parameters, two **s is a dictionary
of additional keyword parameters.

John Roth[color=blue]
>
>[/color]

[David M. Cooke]

Re: Asterisk sign in python

At some point, "John Roth" <newsgroups@jhr othjr.com> wrote:
[color=blue]
> "sarmin" <sarmin_kho@yah oo.com> wrote in message
> news:mailman.15 9.1077796055.85 94.python-list@python.org ...[color=green]
>> Hi Pythoners...
>>
>> It seems to me the Asterisk (*) sign in python means many things...
>>
>> if a python code line looks like this:
>> def__init__(sel f, func, *param):
>> bla bla bla...
>>
>> and then u have something like this:
>> func(*param)
>>
>> and then something like this:
>> def Wrapper(select, func, param):
>> bla bla bla...
>>
>> I took this section of code from the 'Python Cookbook' textbook page
>> 223 about 'Running Functions in the future'...
>>
>> I just cant figure out what is the asterisk (*) sign for and what is
>> the different between *param and param??
>>
>> Many thanks Pythoners...
>>
>> Regards
>> sarmin[/color]
>
> It's for variable length parameter lists. In a function
> definition, one * is a list of additional positional
> parameters, two **s is a dictionary of additional
> keyword parameters.
>
> In a function call, one * is a list of additional
> positional parameters, two **s is a dictionary
> of additional keyword parameters.[/color]

Don't forget multiplicaton:

2 * 2

and power

2 ** 2

:-)

--
|>|\/|<
/--------------------------------------------------------------------------\
|David M. Cooke
|cookedm(at)phy sics(dot)mcmast er(dot)ca

[Myles]

Re: Asterisk sign in python

Hi Sarmin,
[color=blue]
> and then u have something like this:
> func(*param)[/color]
[...][color=blue]
> I just cant figure out what is the asterisk (*) sign for and what is
> the different between *param and param??[/color]

The asterisk is used for multiple parameters, which are passed to
the function as a tuple.

If your function might be called with a varying number of arguments:

myfunc(10)
or
myfunc(10, 20, 30)
or
myfunc(10, "ten", 20, "twenty")

you could write it as:

def myfunc(*param):
print param

and you would get[color=blue][color=green][color=darkred]
>>> myfunc(10)[/color][/color][/color]
(10,)[color=blue][color=green][color=darkred]
>>> myfunc(10, 20, 30)[/color][/color][/color]
(10, 20, 30)[color=blue][color=green][color=darkred]
>>> myfunc(10, "ten", 20, "twenty")[/color][/color][/color]
(10, 'ten', 20, 'twenty')

If you had defined your function without the
asterisk, you could only use a single parameter:

def myfunc(param):
print param
[color=blue][color=green][color=darkred]
>>> myfunc(10)[/color][/color][/color]
10[color=blue][color=green][color=darkred]
>>> myfunc(10, 20, 30)[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#2 7>", line 1, in -toplevel-
myfunc(10, 20, 30)
TypeError: myfunc() takes exactly 1 argument (3 given)

You can have non-optional parameters before the asterisk parameter:

def myfunc(required , necessary, *optional):
print "required", required
print "necessary" , necessary
print "optional", optional
[color=blue][color=green][color=darkred]
>>> myfunc(10, 20, 30, 40)[/color][/color][/color]
required 10
necessary 20
optional (30, 40)[color=blue][color=green][color=darkred]
>>> myfunc(10)[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#3 5>", line 1, in -toplevel-
myfunc(10)
TypeError: myfunc() takes at least 2 arguments (1 given)


Regards, Myles.