Add python-console command to the hint-tester

This enables interactive state exploration of britney's internals for
a given data set.

Signed-off-by: Niels Thykier <niels@thykier.net>

britney.py

@@ -1306,6 +1306,13 @@ class Britney(object):
 
         known_hints = self._hint_parser.registered_hints
 
+        print("Britney hint tester")
+        print()
+        print("Besides inputting known britney hints, the follow commands are also available")
+        print(" * quit/exit      - terminates the shell")
+        print(" * python-console - jump into an interactive python shell (with the current loaded dataset)")
+        print()
+
         while True:
             # read the command from the command line
             try:
@@ -1319,6 +1326,14 @@ class Britney(object):
             # quit the hint tester
             if user_input and user_input[0] in ('quit', 'exit'):
                 break
+            elif user_input and user_input[0] == 'python-console':
+                try:
+                    import britney2.console
+                except ImportError as e:
+                    print("Failed to import britney.console module: %s" % repr(e))
+                    continue
+                britney2.console.run_python_console(self)
+                print("Returning to the britney hint-tester console")
                 # run a hint
             elif user_input and user_input[0] in ('easy', 'hint', 'force-hint'):
                 mi_factory = self._migration_item_factory

britney2/completer.py

@@ -33,7 +33,7 @@ class Completer(object):
         self.cmds = ['easy', 'hint', 'force-hint', 'force', 'remove',
                      'force', 'age-days', 'urgent', 'block-all',
                      'block', 'block-udeb', 'unblock', 'unblock-udeb',
-                     'approve', 'exit', 'quit']
+                     'approve', 'exit', 'quit', 'python-console']
         self.britney = britney
         suite_info = britney.suite_info
         # generate a completion list from excuses.

britney2/console.py

@@ -0,0 +1,32 @@
+import code
+
+
+class SubInterpreterExit(SystemExit):
+    pass
+
+
+def console_quit():
+    raise SubInterpreterExit()
+
+
+def run_python_console(britney_obj):
+    console_locals = {
+        'britney': britney_obj,
+        '__name__': '__console__',
+        '__doc__': None,
+        'quit': console_quit,
+        'exit': console_quit,
+    }
+    console = code.InteractiveConsole(locals=console_locals)
+    banner = """\
+Interactive python (REPL) shell in britney.
+
+Locals available
+ * britney: Instance of the Britney object.
+ * quit()/exit(): leave this REPL console.
+"""
+    try:
+        console.interact(banner=banner, exitmsg='')
+    except SubInterpreterExit:
+        pass
+