[Swig-user] Re: Python overloaded function error message

[Dr. T. M. <tij...@ma...>]

Matthias wrote:

> Python usually outputs something like
>
>   NotImplementedError: No matching function for overloaded =20
>   'RenderState_SetPixelShaderParam'
>
> if it can't find a suitable overload for the function
> in question.

Not necessarily. Take this trivial class:

class Foo {
 private:
   int X, Y;
 public:
   Foo(int id);
   Foo(const char *name);
   void setCoord(int x, int y);
   void setCoord(int x);
};

If you say
=A0 =A0f =3D Foo( 1.2 )
you get the error message
=A0 =A0TypeError: in method 'new_Foo', argument 1 of type 'char const *'

This is rather helpful (though an argument of
type 'int' would actually be fine as well).

However, if you say
=A0 =A0f =3D Foo( 1, 2 )
the dispatcher function generates 'your' error message
=A0 =A0NotImplementedError: No matching function for overloaded 'new_Foo'

Or if you say
   f1 =3D Foo( 1 )
   f1.setCoord( 1, 'two' )
you get a nice error message
   TypeError: in method 'Foo_setCoord', argument 3 of type 'int'

which accurately states which argument is wrong
(argument 3, as 'self' is argument 1).

However, if you say
=A0 =A0f1.setCoord( 1, 2, 3 )
you get the dreaded error message
=A0 =A0NotImplementedError: No matching function for overloaded 'Foo_setCoo=
rd'

This suggests the following pattern:

If a function with the given number of arguments exists,
this is called, and it will produce a fairly exact error
message, stating nicely which argument is wrong.

If no such function exists, the dispatcher function prints
"No matching function ...".

So for our example
   f =3D Foo( 1, 2 )
a more precise error message could be:
=A0 =A0NotImplementedError: wrong number of arguments (2) for
   overloaded function 'new_Foo'

> Maybe this message could be enhanced to tell the user
> the type of the parameter that was passed and probably
> a list of accepted types?=20

How about something like this:
   NotImplementedError: wrong number of arguments (2) for
   overloaded function 'new_Foo'
   Possible prototypes are:
     __init__( id ) # int
     __init__( name ) # str

Or is this too verbose?

=2D Tijs