Functions, Operators, and Overloading?

[Michael Yanowitz]

Hello:

Maybe I am missing something, but from what I've seen,
it is not possible to overload functions in Python. That
is I can't have a
def func1 (int1, string1):
and a
def func1 (int1, int3, string1, string2):
without the second func1 overwriting the first.

However, operators can be overloaded.
So can I define a new operator? If so, can I
define func1 as an operator?

(on the side, I have always wanted to define the
++ operator as +=1. Is that possible?)

Thanks in advance:
Michael Yanowitz

[Brian Beck]

Re: Functions, Operators, and Overloading?

Michael Yanowitz wrote:

Maybe I am missing something, but from what I've seen,
it is not possible to overload functions in Python. That
is I can't have a
def func1 (int1, string1):
and a
def func1 (int1, int3, string1, string2):
without the second func1 overwriting the first.

Correct.

However, operators can be overloaded.
So can I define a new operator? If so, can I
define func1 as an operator?

No. Operators in Python are merely syntax for "magic methods" on the
corresponding type. For instance, x + y would call x.__add__(y). In this
sense you are not really "overloadin g" the operator, you are simply
defining or overwriting its behavior (just like above, where the second
func1 overwrites the previous).

(on the side, I have always wanted to define the
++ operator as +=1. Is that possible?)

No, for the reason above -- there is no magic method associated with ++,
which isn't a real Python operator.

--
Brian Beck
Adventurer of the First Order

[Gerhard Fiedler]

Re: Functions, Operators, and Overloading?

On 2006-07-24 14:30:31, Brian Beck wrote:

Michael Yanowitz wrote:

> Maybe I am missing something, but from what I've seen,
>it is not possible to overload functions in Python. That
>is I can't have a
> def func1 (int1, string1):
> and a
> def func1 (int1, int3, string1, string2):
> without the second func1 overwriting the first.

>
Correct.

Can you write a function that accepts any number of arguments? And then
branch based on the number of arguments supplied?

I guess you can do that with a list as only argument. But can that be done
using the "normal" function argument notation?

Gerhard

[Stefan Behnel]

Re: Functions, Operators, and Overloading?

Gerhard Fiedler schrieb:

On 2006-07-24 14:30:31, Brian Beck wrote:
>

>Michael Yanowitz wrote:

>> Maybe I am missing something, but from what I've seen,
>>it is not possible to overload functions in Python. That
>>is I can't have a
>> def func1 (int1, string1):
>> and a
>> def func1 (int1, int3, string1, string2):
>> without the second func1 overwriting the first.

>Correct.

>
Can you write a function that accepts any number of arguments? And then
branch based on the number of arguments supplied?
>
I guess you can do that with a list as only argument. But can that be done
using the "normal" function argument notation?

I guess you mean something like

func1(int1, arg2, *args):
if len(args) == 2:
...
elif not args:
...
else:
raise ...


Stefan

[bearophileHUGS@lycos.com]

Re: Functions, Operators, and Overloading?

Michael Yanowitz:

Maybe I am missing something, but from what I've seen,
it is not possible to overload functions in Python.

Maybe here you can find some ideas:

http://www.artima.com/forums/flat.jsp?forum=106&thread=101605

http://bob.pythonmac.org/archives/2005/03/30/five-minute-multimethods-in-python-using-dispatch/

http://blog.ianbicking.org/more-on-multimethods.html

(on the side, I have always wanted to define the
++ operator as +=1. Is that possible?)

That's not possible. Maybe you can create an inc() function, similar to
the Pascal one, that with a bit of stack-based magic may increment the
value its called on, but I think this is a bad idea. Leading/trailing
++/-- are quite bad for a language that tries to be clear and to avoid
programmer errors.

Bye,
bearophile

[Gerhard Fiedler]

Re: Functions, Operators, and Overloading?

On 2006-07-24 15:05:53, Stefan Behnel wrote:

>>> Maybe I am missing something, but from what I've seen,
>>>it is not possible to overload functions in Python. That
>>>is I can't have a
>>> def func1 (int1, string1):
>>> and a
>>> def func1 (int1, int3, string1, string2):
>>> without the second func1 overwriting the first.
>>Correct.

>>
>Can you write a function that accepts any number of arguments? And then
>branch based on the number of arguments supplied?
>>
>I guess you can do that with a list as only argument. But can that be done
>using the "normal" function argument notation?

>
I guess you mean something like
>
func1(int1, arg2, *args):
if len(args) == 2:
...
elif not args:
...
else:
raise ...

Exactly. So in a way, the OP's question whether such an overload is
possible has two answers: a formal overload (two separate function
definitions) is not possible, but a functional overload (two definitions
for the different parameter numbers inside one function) is possible.

Thanks,
Gerhard

[Bruno Desthuilliers]

Re: Functions, Operators, and Overloading?

Michael Yanowitz a écrit :

Hello:
>
Maybe I am missing something, but from what I've seen,
it is not possible to overload functions in Python. That
is I can't have a
def func1 (int1, string1):
and a
def func1 (int1, int3, string1, string2):
without the second func1 overwriting the first.

You may want to have a look at Philip Eby's dispatch package. Here's an
introduction:
http://peak.telecommunity.com/DevCen...sitorRevisited

However, operators can be overloaded.
So can I define a new operator?

No.