Where to find good/simple examples for gnatcoll (python)?

Where to find good/simple examples for gnatcoll (python)?

[reinkor]

Hi,

I try to learn fast to use gnatcoll (especially to access python functions).
I would therefore like to have simple examples where an ada program calls
a python script calculating for example 2 + 3 and return 5 (to ada).
Did not directly find this in the documentation included in gnatcoll debian packages.

Somebody any hint?

reinert

Re: Where to find good/simple examples for gnatcoll (python)?

[Vratislav Podzimek]

On Tue, 18 Oct 2016 10:48:17 -0700, reinkor wrote:

> Hi,
> 
> I try to learn fast to use gnatcoll (especially to access python
> functions).
> I would therefore like to have simple examples where an ada program
> calls a python script calculating for example 2 + 3 and return 5 (to
> ada).
> Did not directly find this in the documentation included in gnatcoll
> debian packages.
> 
> Somebody any hint?
> 
> reinert

Maybe http://www.adacore.com/adaanswers/gems/gem-106-lady-ada-kisses-
python-part-2/ could be helpful?

Re: Where to find good/simple examples for gnatcoll (python)?

[reinkor]

Thanks so far, but as I understand, the example here is about the opposite: to access Ada from Python.

reinert

onsdag 19. oktober 2016 10.15.21 UTC+2 skrev Vratislav Podzimek følgende:
> On Tue, 18 Oct 2016 10:48:17 -0700, reinkor wrote:
> 
> > Hi,
> > 
> > I try to learn fast to use gnatcoll (especially to access python
> > functions).
> > I would therefore like to have simple examples where an ada program
> > calls a python script calculating for example 2 + 3 and return 5 (to
> > ada).
> > Did not directly find this in the documentation included in gnatcoll
> > debian packages.
> > 
> > Somebody any hint?
> > 
> > reinert
> 
> Maybe http://www.adacore.com/adaanswers/gems/gem-106-lady-ada-kisses-
> python-part-2/ could be helpful?

Re: Where to find good/simple examples for gnatcoll (python)?

[briot.emmanuel]

If you only want to execute a python script (and perhaps get the output as a
string), you could try:

   Python : constant Scripting_Language :=
       Lookup_Scripting_Language (Repo, "python");
   GNATCOLL.Scripts.Execute_Command (Python, "2 + 3");

Now, if you want to get the result, this is a little more complicated. Assuming you
want to call a foo() function in python, you have to prepare an object with the arguments,
and that will receive the return value.

    Data : Callback_Data'Class := Create (Python, 0);
    Result : Integer;
    Data.Execute_Expression ("2+3");   --  newer versions of gnatcoll
    Result := Data.Return_Value;

or

    Data : Callback_Data'Class := Create (Python, 2);
    Result : Integer;
    Data.Set_Nth_Arg (1, 2);
    Data.Set_Nth_Arg (2, 3);
    Data.Execute_Command ("foo");   --  newer versions of gnatcoll
    Result := Data.Return_Value;

Re: Where to find good/simple examples for gnatcoll (python)?

[reinkor]

Thanks so far. 

My up to date debian jessie seems not yet to include these new features.
However, I tried the program below. It builds, but I get 
"raised CONSTRAINT_ERROR : t1.adb:10 access check failed"

(something goes wring at the line 
"Data   : Callback_Data'Class := Create (Python, 2);")

Any help in my attempt to learn fast is appreciated.


with Ada.Text_IO;             use Ada.Text_IO;
with GNATCOLL.Scripts;        use GNATCOLL.Scripts;
with GNATCOLL.Scripts.Python; use GNATCOLL.Scripts.Python;
with GNATCOLL.Scripts.Shell;  use GNATCOLL.Scripts.Shell;

procedure T1 is

   Repo   : Scripts_Repository  := new Scripts_Repository_Record;
   Python : Scripting_Language  := Lookup_Scripting_Language (Repo, "python");
   Data   : Callback_Data'Class := Create (Python, 2);
   Result : Integer;

begin

   Data.Set_Nth_Arg (1, 2);
   Data.Set_Nth_Arg (2, 3);
   Data.Execute_Command ("./test1.py");   --  newer versions of gnatcoll
   Result := Data.Return_Value;

end T1;

Here is the project file for it:

with "gnatcoll_python";
with "gnatcoll_gmp";
project T1 is
    for Source_Dirs use ("src");
    for Object_Dir use "obj";
    for Exec_Dir use ".";
    for Main use ("t1.adb");
end T1;

reinert

Re: Where to find good/simple examples for gnatcoll (python)?

[briot.emmanuel]

> "raised CONSTRAINT_ERROR : t1.adb:10 access check failed"

This error message tells you quite precisely that the variable Python is null.
And from there we can deduce that ou never registered python as a scripting
language.

You need to call GNATCOLL.Scripts.Python.Register_Python_Scripting.

Check the "Loading the scripting language" section in the GNATCOLL
documentation