(moved from https://sourceforge.net/p/gnudatalanguage/bugs/680/)
As reported on SF by @olebole:

When a GDL routine has an error (for example, a undefined procedure), no exception is thrown, but instead one gets a GDL console:

$ cat pr.py 
import GDL
GDL.pro("rubbish")
$ cat rubbish.pro 
pro rubbish
  bla
end
$ python pr.py 
% Compiled module: RUBBISH.
% RUBBISH: Procedure not found: BLA
% Execution halted at: RUBBISH              2 [...]/rubbish.pro
%                      $MAIN$          
GDL> 

This makes it impossible to handle the problem within Python. Instead, an error should be given back. Ideally, also a Python stacktrace could be created containing the GDL trace as well.