Add missed PyGrid.set_key_value back

pineappl_py/src/grid.rs

@@ -209,6 +209,23 @@ impl PyGrid {
         self.grid.set_remapper(remapper.bin_remapper).unwrap();
     }
 
+    /// Set a metadata key-value pair in the grid.
+    ///
+    /// # Panics
+    /// TODO
+    ///
+    /// Parameters
+    /// ----------
+    /// key : str
+    ///     key
+    /// value : str
+    ///     value
+    pub fn set_key_value(&mut self, key: &str, value: &str) {
+        self.grid
+            .metadata_mut()
+            .insert(key.to_owned(), value.to_owned());
+    }
+
     /// Convolve the grid with as many distributions.
     ///
     /// # Panics

pineappl_py/tests/test_grid.py

@@ -400,6 +400,16 @@ def test_io(self, tmp_path, fake_grids):
         assert isinstance(gg, Grid)
         _ = Grid.read(str(p))
 
+    def test_set_key_value(self, fake_grids):
+        g = fake_grids.grid_with_two_convolutions(
+            channels=CHANNELS,
+            orders=ORDERS,
+            convolutions=[CONVOBJECT, CONVOBJECT],
+        )
+        g.set_key_value("bla", "blub")
+        g.set_key_value('"', "'")
+        g.set_key_value("äöü", "ß\\")
+
     def test_fill(self, fake_grids):
         g = fake_grids.grid_with_two_convolutions(
             channels=CHANNELS,