A question??

[Ishwar Rattan]

I thought that Python has no concept of reference/pointer
(probably incorrect assumption). I saw the following piece of code:

....
def run(program, *args):
pid = os.fork()
if not pid:
os.execvp(program, (program,)+args)
....

and call to run as

run("pyhton", "a.py")

What is the interpretation of *args (in def run(..)?
Looks like a reference to me, so, how does one decide when to use
a reference or not?

Any pointers to info will be appreciated.
-ishwar

 

[Alex Martelli]

I thought that Python has no concept of reference/pointer
(probably incorrect assumption).

No pointers, but any name you use, any slot in a list, any key or value
slot in a dict, etc, IS a reference. Nothing to do with your question
anyway.

def run(program, *args):
pid = os.fork()
if not pid:
os.execvp(program, (program,)+args)

and call to run as

run("pyhton", "a.py")

What is the interpretation of *args (in def run(..)?

It is: 'run' takes any number of positional arguments after the ones
specified so far. Python collects them all into a tuple and your code
refers to that tuple with the name 'args'.

Looks like a reference to me, so, how does one decide when to use
a reference or not?

'args' is a reference just like any other name is.

Any pointers to info will be appreciated.

"Python in a Nutshell", among other reference works, covers argument
passing and such subjects quite well, I think;-).


Alex

 

[Alan Gauld]

def run(program, *args):
pid = os.fork()
if not pid:
os.execvp(program, (program,)+args)

What is the interpretation of *args (in def run(..)?
Looks like a reference to me, so, how does one decide when to use
a reference or not?

Its not a reference its a placeholder for an unspecified number
of arguments. (Actually I think it's technically a tuple of
arguments?) You can think of it like the C va_arg construct
used for functions like printf().

There is also a **args construct which is for a dictionary of
keyword arguments. I'm no expert on these but thats what they are
about.

Here is the url to the documentation:

http://docs.python.org/ref/function.html

HTH,

Alan G.

Author of the Learn to Program website
http://www.freenetpages.co.uk/hp/alan.gauld