make Geldschieberbot a context manager

Previosuly there was the problem that the state was saved when the
bot object was destructed.
When there was an unhandled exception it was possible for the builtins
to be cleanedup before the bot's destructor was executed resulting
in yet another exception because the open builtin was no longer
available.

This is no longer possible when the bot is used as a context manager
python guarantees that the __exit__ code is executed before leaving
the with block.

This allows us prevent the state from beeing saved when there was an
exception to prevent invalid states.

3 files changed, 26 insertions, 24 deletions

diff --git a/geldschieberbot.py b/geldschieberbot.py
index 046d543..ff859f0 100644
--- a/geldschieberbot.py
+++ b/geldschieberbot.py
@@ -1009,8 +1009,6 @@ class Geldschieberbot:
         self.dry_run = dry_run  # Run without changing the stored state
         self.record_changes = True  # Should changes be recorded
 
-        self.load_state()
-
         # Command dispatch table
         self.cmds = {
             'reg': self.register,
@@ -1046,8 +1044,13 @@ class Geldschieberbot:
             'thanks': self.thanks,
         }
 
-    def __del__(self):
-        self.save_state()
+    def __enter__(self):
+        self.load_state()
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        if not exc_type:
+            self.save_state()
 
     def enable_dry_run(self) -> bool:
         """Enable dry run"""
diff --git a/single_shot.py b/single_shot.py
index 41d9849..0c85947 100755
--- a/single_shot.py
+++ b/single_shot.py
@@ -80,24 +80,23 @@ def main():
     if not group_id:
         die('A group id must be provided')
 
-    bot = Geldschieberbot(state_path, group_id, dry_run=args.dry_run)
-
-    # Read cmds from stdin
-    for line in sys.stdin.read().splitlines():
-        try:
-            envelope = json.loads(line)['envelope']
-        except json.JSONDecodeError:
-            print(datetime.now(), line, "not valid json")
-            continue
-
-        quote = None
-        if not args.no_quote:
-            quote = Quote(timestamp=envelope['timestamp'],
-                          author=envelope['source'])
-
-        send(send_cmd, bot.handle(envelope), quote)
-
-    send(send_cmd, bot.run_scheduled_cmds())
+    with Geldschieberbot(state_path, group_id, dry_run=args.dry_run) as bot:
+        # Read cmds from stdin
+        for line in sys.stdin.read().splitlines():
+            try:
+                envelope = json.loads(line)['envelope']
+            except json.JSONDecodeError:
+                print(datetime.now(), line, "not valid json")
+                continue
+
+            quote = None
+            if not args.no_quote:
+                quote = Quote(timestamp=envelope['timestamp'],
+                              author=envelope['source'])
+
+            send(send_cmd, bot.handle(envelope), quote)
+
+        send(send_cmd, bot.run_scheduled_cmds())
 
 
 if __name__ == "__main__":
diff --git a/test.py b/test.py
index f392a4d..8535485 100755
--- a/test.py
+++ b/test.py
@@ -1417,8 +1417,8 @@ class TestStateLoadStore(unittest.TestCase):
 
     def test_init(self):
         sp = "test/state_3users.json"
-        bot = Geldschieberbot(sp, DEFAULT_GROUP_ID)
-        self.assertTrue(compare_state(sp, state=bot.state))
+        with Geldschieberbot(sp, DEFAULT_GROUP_ID) as bot:
+            self.assertTrue(compare_state(sp, state=bot.state))
 
     def test_explicit_load(self):
         sp = "test/state_3users.json"