Add default parameter geom_blank to stat

plotnine/geoms/geom.py

@@ -118,7 +118,7 @@ def from_stat(stat: stat) -> geom:
         PlotnineError
             If unable to create a `geom`.
         """
-        name = stat.params["geom"]
+        name = stat.params.get("geom", "blank")
 
         if isinstance(name, geom):
             return name
@@ -494,18 +494,21 @@ def _verify_arguments(self, kwargs: dict[str, Any]):
         geom_stat_args = kwargs.keys() | self._stat._kwargs.keys()
         unknown = (
             geom_stat_args
-            - self.aesthetics()
-            - self.DEFAULT_PARAMS.keys()  # geom aesthetics
-            - self._stat.aesthetics()  # geom parameters
-            - self._stat.DEFAULT_PARAMS.keys()  # stat aesthetics
-            - {  # stat parameters
+            - self.aesthetics()  # geom aesthetics
+            - self.DEFAULT_PARAMS.keys()  # geom parameters
+            - self._stat.aesthetics()  # stat aesthetics
+            - self._stat.DEFAULT_PARAMS.keys()  # stat parameters
+            - {
+                # stat parameters
                 "data",
                 "mapping",
-                "show_legend",  # layer parameters
+                "geom",
+                # layer parameters
+                "show_legend",
                 "inherit_aes",
                 "raster",
             }
-        )  # layer parameters
+        )
         if unknown:
             msg = (
                 "Parameters {}, are not understood by "

plotnine/stats/stat.py

@@ -42,7 +42,7 @@ class stat(ABC, metaclass=Register):
     NON_MISSING_AES: set[str] = set()
     """Required aesthetics for the stat"""
 
-    DEFAULT_PARAMS: dict[str, Any] = {}
+    DEFAULT_PARAMS: dict[str, Any] = {"geom": "blank"}
     """Required parameters for the stat"""
 
     CREATES: set[str] = set()

tests/test_stat.py

@@ -62,6 +62,18 @@ def draw(pinfo, panel_params, coord, ax, **kwargs):
     assert "weight" in g._stat.params
 
 
+def test_stat_extending():
+    class stat_xyz(stat):
+        REQUIRED_AES = {"x", "y"}
+
+        def compute_group(self, data, scales):
+            return data
+
+    p = ggplot(mtcars, aes("wt", "mpg")) + stat_xyz(geom="point", size=1)
+
+    p.draw_test()  # pyright: ignore[reportAttributeAccessIssue]
+
+
 def test_calculated_expressions():
     p = ggplot(mtcars, aes(x="factor(cyl)", y="..count..+1")) + geom_bar()
     # No exception