BUG: return itself when no change possible in remove_false_nodes

momepy/preprocessing.py

@@ -190,6 +190,8 @@ def remove_false_nodes(gdf):
     """
     Clean topology of existing LineString geometry by removal of nodes of degree 2.
 
+    Returns the original gdf if there's no node of degree 2.
+
     Parameters
     ----------
     gdf : GeoDataFrame, GeoSeries, array of pygeos geometries
@@ -276,6 +278,9 @@ def remove_false_nodes(gdf):
             )
         return df.append(final, ignore_index=True)
 
+    # if there's nothing to fix, return the original dataframe
+    return gdf
+
 
 class CheckTessellationInput:
     """

tests/test_preprocess.py

@@ -4,6 +4,7 @@
 from packaging.version import Version
 from shapely import affinity
 from shapely.geometry import LineString, MultiPoint, Polygon
+from geopandas.testing import assert_geodataframe_equal
 
 import momepy as mm
 
@@ -47,6 +48,10 @@ def test_remove_false_nodes(self):
         assert isinstance(fixed, gpd.GeoDataFrame)
         assert sorted(self.false_network.columns) == sorted(fixed.columns)
 
+        # no node of a degree 2
+        df = self.df_streets.drop([4, 7, 17, 22])
+        assert_geodataframe_equal(df, mm.remove_false_nodes(df))
+
     def test_CheckTessellationInput(self):
         df = self.df_buildings
         df.loc[144, "geometry"] = Polygon([(0, 0), (0, 1), (1, 0)])