python: implement twa_graph.__copy__

Fixes #470, suggested by Cambridge Yang.

* python/spot/__init__.py (twa_graph.__copy__): Call make_twa_graph.
* tests/python/twagraph.py: Test it.
* NEWS: Mention it.

NEWS

@@ -235,7 +235,10 @@ New in spot 2.9.7.dev (not yet released)
     See https://spot.lrde.epita.fr/ipynb/games.html for examples.
 
   - spot::twa::prop_set was previously abstent from the Python
-    binding.  It is now available as spot.twa_prop_set (issue #453).
+    bindings, making it impossible to call make_twa_graph() for copying
+    a twa.  It is now available as spot.twa_prop_set (issue #453).
+    Also for convenience, the twa_graph.__copy__() method, called by
+    copy.copy(), will duplicate a twa_graph (issue #470).
 
   Bugs fixed:
 

python/spot/__init__.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Copyright (C) 2014-2020  Laboratoire de
+# Copyright (C) 2014-2021  Laboratoire de
 # Recherche et Développement de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -221,6 +221,9 @@ class twa_graph:
         from spot.jupyter import SVG
         return SVG(_ostream_to_svg(ostr))
 
+    def __copy__(self):
+        return make_twa_graph(self, twa_prop_set.all())
+
 
 def make_twa_graph(*args):
     from spot.impl import make_twa_graph as mtg

tests/python/twagraph.py

@@ -44,7 +44,7 @@ except ValueError as e:
 aut.new_states(3)
 aut.set_init_state(2)
 assert aut.get_init_state_number() == 2
-e = aut.set_univ_init_state([2, 1])
+aut.set_univ_init_state([2, 1])
 assert [2, 1] == list(aut.univ_dests(aut.get_init_state_number()))
 
 try:
@@ -67,6 +67,13 @@ cpy = spot.make_twa_graph(aut, spot.twa_prop_set(False, False, False,
 assert cpy.prop_universal() != aut.prop_universal()
 assert cpy.prop_universal() == spot.trival.maybe()
 
+from copy import copy
+cpy = copy(aut)
+assert aut.to_str() == cpy.to_str()
+cpy.set_init_state(1)
+assert [2, 1] == list(aut.univ_dests(aut.get_init_state_number()))
+assert cpy.get_init_state_number() == 1
+
 try:
     s = aut.state_acc_sets(0)
 except RuntimeError as e: