Add option to add metadata to artifacts

A dict with custom metadata can now be added to artifacts. This only has
an effect for the MongoObserver. The metadata will appear in the
`.metadata` attribute of the file like objects retrieved with pymongo
from gridfs.

sacred/experiment.py

@@ -321,7 +321,7 @@ def add_resource(self, filename):
         assert self.current_run is not None, "Can only be called during a run."
         self.current_run.add_resource(filename)
 
-    def add_artifact(self, filename, name=None):
+    def add_artifact(self, filename, name=None, metadata=None):
         """Add a file as an artifact.
 
         In Sacred terminology an artifact is a file produced by the experiment
@@ -338,10 +338,12 @@ def add_artifact(self, filename, name=None):
         name : str, optional
             optionally set the name of the artifact.
             Defaults to the relative file-path.
-
+        metadata: dict, optional
+            optionally attach metadata to the artifact.
+            This only has an effect when using the MongoObserver.
         """
         assert self.current_run is not None, "Can only be called during a run."
-        self.current_run.add_artifact(filename, name)
+        self.current_run.add_artifact(filename, name, metadata)
 
     @property
     def info(self):

sacred/observers/mongo.py

@@ -184,12 +184,12 @@ def resource_event(self, filename):
         self.run_entry['resources'].append((filename, md5hash))
         self.save()
 
-    def artifact_event(self, name, filename):
+    def artifact_event(self, name, filename, metadata=None):
         with open(filename, 'rb') as f:
             run_id = self.run_entry['_id']
             db_filename = 'artifact://{}/{}/{}'.format(self.runs.name, run_id,
                                                        name)
-            file_id = self.fs.put(f, filename=db_filename)
+            file_id = self.fs.put(f, filename=db_filename, metadata=metadata)
         self.run_entry['artifacts'].append({'name': name,
                                             'file_id': file_id})
         self.save()

sacred/run.py

@@ -157,7 +157,7 @@ def add_resource(self, filename):
         filename = os.path.abspath(filename)
         self._emit_resource_added(filename)
 
-    def add_artifact(self, filename, name=None):
+    def add_artifact(self, filename, name=None, metadata=None):
         """Add a file as an artifact.
 
         In Sacred terminology an artifact is a file produced by the experiment
@@ -173,10 +173,13 @@ def add_artifact(self, filename, name=None):
         name : str, optional
             optionally set the name of the artifact.
             Defaults to the filename.
+        metadata: dict
+            optionally attach metadata to the artifact.
+            This only has an effect when using the MongoObserver.
         """
         filename = os.path.abspath(filename)
         name = os.path.basename(filename) if name is None else name
-        self._emit_artifact_added(name, filename)
+        self._emit_artifact_added(name, filename, metadata)
 
     def __call__(self, *args):
         r"""Start this run.
@@ -374,11 +377,12 @@ def _emit_resource_added(self, filename):
         for observer in self.observers:
             self._safe_call(observer, 'resource_event', filename=filename)
 
-    def _emit_artifact_added(self, name, filename):
+    def _emit_artifact_added(self, name, filename, metadata):
         for observer in self.observers:
             self._safe_call(observer, 'artifact_event',
                             name=name,
-                            filename=filename)
+                            filename=filename,
+                            metadata=metadata)
 
     def _safe_call(self, obs, method, **kwargs):
         if obs not in self._failed_observers and hasattr(obs, method):

tests/test_run.py

@@ -129,8 +129,9 @@ def test_run_heartbeat_event(run):
 def test_run_artifact_event(run):
     observer = run.observers[0]
     handle, f_name = tempfile.mkstemp()
-    run.add_artifact(f_name, name='foobar')
-    observer.artifact_event.assert_called_with(filename=f_name, name='foobar')
+    metadata = {'testkey': 42}
+    run.add_artifact(f_name, name='foobar', metadata=metadata)
+    observer.artifact_event.assert_called_with(filename=f_name, name='foobar', metadata=metadata)
     os.close(handle)
     os.remove(f_name)