argument type

It's me itsme at yahoo.com
Tue Dec 28 06:41:23 CET 2004


Steve,

The argument I wish to pass is either one string, or a list of strings, or a
tuple of strings.

For instance, I have:

    def abc(arg1, arg2, arg3)

Let say that I expect arg1 and arg3 to be a number, and arg2 can be either
one string, or a bunch of strings and I need to do something on each of the
strings passed down.  So, using the isinstance function suggested, I can
have:

    def abc(arg1, arg2, arg3)
        if isinstance(arg2,(list,tuple)):
            for item in arg2:
                abc(arg1, item)
        else:
            # do whatever with arg2 and I know now arg2 is a single instance
of a string
    ...

This way, when I invoke the function, I don't have to always remember the []
like:

    abc(1,["String 1",],5)

I can simply do:

    abc(1,"String 1",5)

and likewise, I can do:

    abc(1,["String 1","String 2"],5)

Am I on the right track?


"Steven Bethard" <steven.bethard at gmail.com> wrote in message
news:hd6Ad.244202$5K2.52003 at attbi_s03...
> It's me wrote:
> > A newbie question.
> >
> > How can I tell from within a function whether a particular argument is a
> > sigular type, or a complex type?
> >
> > For instance, in:
> >
> >     def abc(arg1)
> >
> > How do I know if arg1 is a single type (like a number), or a list?
> >
> > In C++, you would do it with function overloading.  If arg1 is always
simple
> > type, I wouldn't care what it is.  But what if I *do* need to know
whether
> > arg1 is a list or not?
> >
> > I hate to have to have 2 functions: 1 for simple types, and one for list
> > types and then do something like:
> >
> >     abc_simple(1.0)
> >     abc_list([1.0,2.0])
> >
>
> Generally, if I have a function that might take one or more args, I'd
> write it like:
>
>      def abc(*args)
>
> and then call it with one of the following:
>
>      abc(1.0)
>      abc(1.0, 2.0)
>      abc(*[1.0, 2.0])
>
> If you're really stuck with the one argument signature, I tend towards
> the "ask forgiveness rather than permission" instead of the "look before
> you leap" style.  Something like:
>
>      def abc(arg1):
>          try:
>              x = iter(arg1)
>          except TypeError:
>              x = iter([arg1])
>          # now do whatever you want with x
>
> Note that this might give you some problems if you want to pass in
> strings (since they're iterable).  Can you give some more specifics on
> the problem?  What is the actual function you want to write and what
> kind of arguments to you expect to receive?
>
> Steve





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