Velocity Reviews > function that accepts any amount of arguments?

# function that accepts any amount of arguments?

globalrev
Guest
Posts: n/a

 04-24-2008
if i want a function that can take any amount of arguments how do i
do?

lets say i want a function average that accepts any number of integers
and returns the average.

Paul McNett
Guest
Posts: n/a

 04-24-2008
globalrev wrote:
> if i want a function that can take any amount of arguments how do i
> do?

Put an asterisk before the argument name.

> lets say i want a function average that accepts any number of integers
> and returns the average.

def avg(*args):
return sum(args) / len(args)

There are some dangers (at least two glaring ones) with this code,
though, which I leave as an exercise for the reader.

Paul

Steve Holden
Guest
Posts: n/a

 04-24-2008
globalrev wrote:
> if i want a function that can take any amount of arguments how do i
> do?
>
> lets say i want a function average that accepts any number of integers
> and returns the average.

Use a parameter of the form *args - the asterisk tells the interpreter
to collect positional arguments into a tuple. Untested:

def mean(*x):
total = 0.0
for v in x:
total += v
return v/len(x)

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/

Terry Reedy
Guest
Posts: n/a

 04-24-2008

"globalrev" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
| if i want a function that can take any amount of arguments how do i
| do?
|
| lets say i want a function average that accepts any number of integers
| and returns the average.

Steve Holden
Guest
Posts: n/a

 04-24-2008
Ken wrote:
> "Steve Holden" <(E-Mail Removed)> wrote in message

[...]
>> def mean(*x):
>> total = 0.0
>> for v in x:
>> total += v
>> return v/len(x)
>>

>
> think you want total/len(x) in return statement
>

Yes indeed, how glad I am I wrote "untested". I clearly wasn't pair
programming when I wrote this post

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/

Bruno Desthuilliers
Guest
Posts: n/a

 04-24-2008
Paul McNett a écrit :
>
> def avg(*args):
> return sum(args) / len(args)
>
> There are some dangers (at least two glaring ones) with this code,
> though, which I leave as an exercise for the reader.

try:
avg("toto", 42)
except TypeError, e:
print "this is the first one : %s" % e
try:
avg()
except ZeroDivisionError, e:
print "this is the second : %s" % e

As far as I'm concerned, I would not handle the first one in the avg
function - just document that avg expects numeric args.

Not quite sure what's the best thing to do in the second case - raise a
ValueError if args is empty, or silently return 0.0 - but I'd tend to
choose the first solution (Python's Zen, verses 9-11).

malkarouri
Guest
Posts: n/a

 04-24-2008
On Apr 24, 12:43*pm, Bruno Desthuilliers <bruno.
(E-Mail Removed)> wrote:
[...]
> Not quite sure what's the best thing to do in the second case - raise a
> ValueError if args is empty, or silently return 0.0 - but I'd tend to
> choose the first solution (Python's Zen, verses 9-11).

What's wrong with raising ZeroDivisionError (not stopping the
exception in the first place)?

k

Jonathan Gardner
Guest
Posts: n/a

 04-24-2008
On Apr 24, 5:28*am, malkarouri <(E-Mail Removed)> wrote:
>
> What's wrong with raising ZeroDivisionError (not stopping the
> exception in the first place)?
>

Because when I use your module, call avg (or mean) without args, I
should see an error that says, "Hey, you have to pass at least one
value in!"

ZeroDivisonError doesn't mean that. It means I tried to divide by
zero. Naively, I don't see where I was dividing by zero (because I
don't remember how to calculate the mean---that's what your code was
for.)

ValueError does mean that I didn't pass the right kind of arguments
in. ValueError("No items specified") would be even clearer. (Or maybe
TypeError?)

In general, any exception thrown should be meaningful to the code you
are throwing it to. That means they aren't familiar with how your code
works.

Steve Holden
Guest
Posts: n/a

 04-24-2008
Jonathan Gardner wrote:
> On Apr 24, 5:28 am, malkarouri <(E-Mail Removed)> wrote:
>> What's wrong with raising ZeroDivisionError (not stopping the
>> exception in the first place)?
>>

>
> Because when I use your module, call avg (or mean) without args, I
> should see an error that says, "Hey, you have to pass at least one
> value in!"
>
> ZeroDivisonError doesn't mean that. It means I tried to divide by
> zero. Naively, I don't see where I was dividing by zero (because I
> don't remember how to calculate the mean---that's what your code was
> for.)
>
> ValueError does mean that I didn't pass the right kind of arguments
> in. ValueError("No items specified") would be even clearer. (Or maybe
> TypeError?)
>
> In general, any exception thrown should be meaningful to the code you
> are throwing it to. That means they aren't familiar with how your code
> works.
>

This is Advice. Software Engineering's next door

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/

bruno.desthuilliers@gmail.com
Guest
Posts: n/a

 04-24-2008
On 24 avr, 14:28, malkarouri <(E-Mail Removed)> wrote:
> On Apr 24, 12:43 pm, Bruno Desthuilliers <(E-Mail Removed)> wrote:
>
> [...]
>
> > Not quite sure what's the best thing to do in the second case - raise a
> > ValueError if args is empty, or silently return 0.0 - but I'd tend to
> > choose the first solution (Python's Zen, verses 9-11).

>
> What's wrong with raising ZeroDivisionError (not stopping the
> exception in the first place)?

Because - from a semantic POV - the real error is not that you're
trying to divide zero by zero, but that you failed to pass any
argument. FWIW, I'd personnaly write avg as taking a sequence - ie,
not using varargs - in which case calling it without arguments would a
TypeError (so BTW please s/Value/Type/ in my previous post).