COMPAT: Alias isnull -> isna, following pandas (geopandas#517)

* COMPAT: Alias isnull -> isna, following pandas

Add same alias for notnull -> notna, and add tests of empty geometries
to ensure that the check is working for the case it is supposed to
catch.

geopandas/geoseries.py

@@ -168,12 +168,50 @@ def copy(self, order='C'):
         return GeoSeries(self.values.copy(order), index=self.index,
                       name=self.name).__finalize__(self)
 
-    def isnull(self):
-        """Null values in a GeoSeries are represented by empty geometric objects"""
+    def isna(self):
+        """
+        N/A values in a GeoSeries can be represented by empty geometric
+        objects, in addition to standard representations such as None and
+        np.nan.
+
+        Returns
+        -------
+        A boolean pandas Series of the same size as the GeoSeries,
+        True where a value is N/A.
+
+        See Also
+        --------
+        GeoSereies.notna : inverse of isna
+        """
         non_geo_null = super(GeoSeries, self).isnull()
         val = self.apply(_is_empty)
         return np.logical_or(non_geo_null, val)
 
+    def isnull(self):
+        """Alias for `isna` method. See `isna` for more detail."""
+        return self.isna()
+
+    def notna(self):
+        """
+        N/A values in a GeoSeries can be represented by empty geometric
+        objects, in addition to standard representations such as None and
+        np.nan.
+
+        Returns
+        -------
+        A boolean pandas Series of the same size as the GeoSeries,
+        False where a value is N/A.
+
+        See Also
+        --------
+        GeoSeries.isna : inverse of notna
+        """
+        return ~self.isna()
+
+    def notnull(self):
+        """Alias for `notna` method. See `notna` for more detail."""
+        return self.notna()
+
     def fillna(self, value=None, method=None, inplace=False,
                **kwargs):
         """Fill NA/NaN values with a geometry (empty polygon by default).

geopandas/tests/test_pandas_methods.py

@@ -7,7 +7,7 @@
 import numpy as np
 import pandas as pd
 import shapely
-from shapely.geometry import Point
+from shapely.geometry import Point, Polygon
 
 from geopandas import GeoDataFrame, GeoSeries
 from geopandas.tests.util import assert_geoseries_equal
@@ -176,14 +176,18 @@ def test_dropna():
     assert_geoseries_equal(res, exp)
 
 
-def test_isnull():
-    for NA in [None, np.nan]:
-        s2 = GeoSeries([Point(0, 0), NA, Point(2, 2)])
-        res = s2.isnull()
-        exp = pd.Series([False, True, False])
-        assert_series_equal(res, exp)
-        res = s2.notnull()
-        assert_series_equal(res, ~exp)
+@pytest.mark.parametrize("NA", [None, np.nan, Point(), Polygon()])
+def test_isna(NA):
+    s2 = GeoSeries([Point(0, 0), NA, Point(2, 2)])
+    exp = pd.Series([False, True, False])
+    res = s2.isnull()
+    assert_series_equal(res, exp)
+    res = s2.isna()
+    assert_series_equal(res, exp)
+    res = s2.notnull()
+    assert_series_equal(res, ~exp)
+    res = s2.notna()
+    assert_series_equal(res, ~exp)
 
 
 # Groupby / algos