#  SumGTK.py  (c) Kari Laitinen

#  http://www.naturalprogramming.com

#  The development of this program has been sponsored by Nokia Multimedia.

#  2006-09-11  File created.
#  2006-09-14  Last modification.

#  This program demonstrates the following things:
#    --  using a Table for placing widgets in a window
#    --  using class Entry for creating editable text fields
#    --  using class Label for creating non-editable texts

import gtk

class Sum :

   def __init__( self ) :

      self.application_window = gtk.Window( gtk.WINDOW_TOPLEVEL )
      self.application_window.set_title( "CALCULATE THE SUM OF TWO INTEGERS" )
      self.application_window.connect("destroy", lambda w: gtk.main_quit() )

      self.application_window.set_size_request( 600, 300 )

      self.first_text_field   =  gtk.Entry()
      self.first_text_field.connect( "changed", self.text_field_text_changed,
                                self.first_text_field )
      self.first_text_field.set_alignment( 1.0 )  #  right-justified text field
      self.first_text_field.set_width_chars( 15 )

      self.second_text_field  =  gtk.Entry()
      self.second_text_field.connect( "changed", self.text_field_text_changed,
                                 self.second_text_field )
      self.second_text_field.set_alignment( 1.0 )  # right-justified text field

      first_integer_label   =  gtk.Label( "First integer:" )
      first_integer_label.set_alignment( 0.0, 0.5 )  #  left-justified
      second_integer_label  =  gtk.Label( "Second integer:" )
      second_integer_label.set_alignment( 0.0, 0.5 )  #  left-justified
      calculated_sum_label  =  gtk.Label( "Calculated sum:" )
      calculated_sum_label.set_alignment( 0.0, 0.5 )  #  left-justified

      self.result_label  =  gtk.Label( "0" )
      self.result_label.set_alignment( 1.0, 0.5 )

      #  The table_for_widgets is larger than is necessary for
      #  placing the widgets. The table cells near the window
      #  border are left empty. Thus the widgets (labels and text
      #  entry fields appear at the center of the window).
      #  The third parameter "True" makes the table homogenous,
      #  which means that all table cells are of equal size.

      table_for_widgets  =  gtk.Table( 5, 4, True )

      table_for_widgets.attach( first_integer_label,    1, 2, 1, 2 )
      table_for_widgets.attach( self.first_text_field,  2, 3, 1, 2 )
      table_for_widgets.attach( second_integer_label,   1, 2, 2, 3 )
      table_for_widgets.attach( self.second_text_field, 2, 3, 2, 3 )
      table_for_widgets.attach( calculated_sum_label,   1, 2, 3, 4 )
      table_for_widgets.attach( self.result_label,      2, 3, 3, 4 )

      self.application_window.add( table_for_widgets )

      self.first_text_field.show()
      self.second_text_field.show()

      first_integer_label.show()
      second_integer_label.show()
      calculated_sum_label.show()
      self.result_label.show()

      table_for_widgets.show()
      self.application_window.show()

   def text_field_text_changed( self, widget, text_field=None ) :

      first_text   =  self.first_text_field.get_text()
      second_text  =  self.second_text_field.get_text()

      #  The following two if constructs ensure that empty text fields
      #  are treated as if they contained a zero.

      if  len( first_text )  ==  0 :

         first_text  =  "0"

      if  len( second_text )  ==  0 :

         second_text  =  "0"

      #  An exception will be thrown (raised) if either of the texts
      #  represent of a non-int value.

      try :

         first_integer   =  int( first_text )
         second_integer  =  int( second_text )

         self.result_label.set_text( str( first_integer + second_integer ) )

      except :

         self.result_label.set_text( "INPUT ERROR!" )


   def run( self ) :
      gtk.main()

if __name__ == "__main__":
   this_application  =  Sum()
   this_application.run()