fix geopandas inheritance

Author: christophfink

CHANGELOG.md

@@ -1,3 +1,8 @@
+- **1.0.2** (2026-01-16):
+    - BREAKING: require cartogram_attribute to be a positional argument
+    - fix inheritance from geopandas.GeoDataFrame
+    - update geopandas dependency
+
 - **1.0.1** (2025-06-27):
     - workaround for change in geopandas inheritance
 

pyproject.toml

@@ -12,7 +12,7 @@ authors = [
 ]
 
 dependencies = [
-    "geopandas<1.1.0",
+    "geopandas",
     "joblib",
     "numpy",
     "pandas",

src/cartogram/__init__.py

@@ -2,7 +2,7 @@
 
 """Compute continuous cartograms."""
 
-__version__ = "1.0.1"
+__version__ = "1.0.2"
 
 from .cartogram import Cartogram
 

src/cartogram/cartogram.py

@@ -34,9 +34,33 @@
 class Cartogram(geopandas.GeoDataFrame):
     """Compute continuous cartograms."""
 
+    _constructor = geopandas.GeoDataFrame
+
+    _constructor_sliced = pandas.Series
+
+    @classmethod
+    def _geodataframe_constructor_with_fallback(
+        cls, *args, **kwargs
+    ):
+        """
+        A flexible constructor for Cartogram.
+
+        It which checks whether or not arguments of the child class are used.
+        """
+        if "cartogram_attribute" in kwargs.keys():
+            df = cls(*args, **kwargs)
+        else:
+            df = geopandas.GeoDataFrame(*args, **kwargs)
+            geometry_cols_mask = df.dtypes == "geometry"
+            if len(geometry_cols_mask) == 0 or geometry_cols_mask.sum() == 0:
+                df = pandas.DataFrame(df)
+
+        return df
+
     def __init__(
         self,
         input_polygon_geodataframe,
+        /,
         cartogram_attribute,
         max_iterations=10,
         max_average_error=0.1,