chore: deprecate basemap backend starting from version 3.0

docs/projections.py

@@ -289,11 +289,10 @@
 #      when they are omitted (e.g., ``lon0=0`` as the default for most projections).
 #
 # .. warning::
-#    The `basemap`_ package is now being actively maintained again with a short hiatus for a few years. We originally
-#    included basemap support because its gridline labeling was more powerful
-#    than cartopy gridline labeling. While cartopy gridline labeling has
-#    significantly improved since version 0.18, UltraPlot continues to support
-#    both mapping libraries to give users flexibility in their visualization choices.
+#    The basemap backend is deprecated as of version 3.0.0 and may be removed in a
+#    future release. Please use the cartopy backend instead. Cartopy gridline
+#    labeling has significantly improved since version 0.18 and now covers the
+#    features we originally included basemap support for.
 
 # %%
 import ultraplot as uplt

ultraplot/_subplots.py

@@ -66,10 +66,7 @@ def parse_backend(backend=None, basemap=None):
         Handle deprecation of basemap and cartopy package.
         """
         if backend == "basemap":
-            warnings._warn_ultraplot(
-                f"{backend=} will be deprecated in next major release (v2.0). "
-                "See https://github.com/Ultraplot/ultraplot/pull/243"
-            )
+            constructor._warn_basemap_deprecated()
         return backend
 
     def parse_proj(
@@ -108,6 +105,7 @@ def parse_proj(
             ):
                 name = "ultraplot_basemap"
                 kwargs["map_projection"] = proj
+                constructor._warn_basemap_deprecated()
 
         if name is None and isinstance(proj, str):
             try:

ultraplot/axes/base.py

@@ -104,6 +104,10 @@
 backend : {'cartopy', 'basemap'}, default: :rc:`geo.backend`
     Whether to use `~mpl_toolkits.basemap.Basemap` or
     `~cartopy.crs.Projection` for map projections.
+
+    .. deprecated:: 3.0.0
+        The ``'basemap'`` backend is deprecated and may be removed in a
+        future release. Please use the ``'cartopy'`` backend instead.
 """
 docstring._snippet_manager["axes.proj"] = _proj_docstring
 docstring._snippet_manager["axes.proj_kw"] = _proj_kw_docstring

ultraplot/constructor.py

@@ -1484,6 +1484,17 @@ def Scale(scale, *args, **kwargs):
     return scale(*args, **kwargs)
 
 
+def _warn_basemap_deprecated():
+    """
+    Warn that the basemap backend is deprecated.
+    """
+    warnings._warn_ultraplot(
+        "The basemap backend was deprecated in version 3.0.0 and may be removed "
+        "in a future release. Please use the cartopy backend instead. "
+        "See https://github.com/Ultraplot/ultraplot/pull/243"
+    )
+
+
 def Proj(
     name,
     backend=None,
@@ -1574,6 +1585,10 @@ def Proj(
     backend : {'cartopy', 'basemap'}, default: :rc:`geo.backend`
         Whether to return a cartopy `~cartopy.crs.Projection` instance
         or a basemap `~mpl_toolkits.basemap.Basemap` instance.
+
+        .. deprecated:: 3.0.0
+            The ``'basemap'`` backend is deprecated and may be removed in a
+            future release. Please use the ``'cartopy'`` backend instead.
     lon0, lat0 : float, optional
         The central projection longitude and latitude. These are translated to
         `central_longitude`, `central_latitude` for cartopy projections.
@@ -1670,6 +1685,8 @@ def Proj(
                 f"Unexpected projection {name!r}. Must be PROJ string name, "
                 "cartopy.crs.Projection, or mpl_toolkits.basemap.Basemap."
             )
+        if backend == "basemap":
+            _warn_basemap_deprecated()
     for key_proj, key_cartopy, value in (
         ("lon_0", "central_longitude", lon0),
         ("lat_0", "central_latitude", lat0),
@@ -1692,6 +1709,8 @@ def Proj(
             warnings._warn_ultraplot(f"Ignoring Proj() keyword arg(s): {kwargs!r}.")
         proj = name
         backend = "cartopy" if is_crs else "basemap"
+        if is_basemap:
+            _warn_basemap_deprecated()
 
     # Cartopy name
     # NOTE: Error message matches basemap invalid projection message

ultraplot/internals/rcsetup.py

@@ -1764,7 +1764,9 @@ def _validator_accepts(validator, value):
         "cartopy",
         _validate_belongs("cartopy", "basemap"),
         "The backend used for `~ultraplot.axes.GeoAxes`. Must be "
-        "either 'cartopy' or 'basemap'.",
+        "either 'cartopy' or 'basemap'. "
+        ".. deprecated:: 3.0.0 The 'basemap' backend is deprecated and may be "
+        "removed in a future release. Please use 'cartopy' instead.",
     ),
     "geo.extent": (
         "globe",

ultraplot/tests/test_constructor_helpers_extra.py

@@ -2,6 +2,7 @@
 """Additional branch coverage for constructor helpers."""
 
 import importlib
+import warnings
 
 import cycler
 import matplotlib.colors as mcolors
@@ -195,3 +196,35 @@ def test_proj_constructor_branches():
         constructor.Proj("merc", backend="cartopy", round=True)
     with pytest.raises(ValueError, match="unknown cartopy projection class"):
         constructor.Proj("not-a-proj", backend="cartopy")
+
+
+def test_proj_basemap_backend_deprecated():
+    pytest.importorskip("mpl_toolkits.basemap")
+    with pytest.warns(UltraPlotWarning, match="deprecated in version 3\\.0\\.0"):
+        proj = constructor.Proj("npstere", backend="basemap")
+    assert proj._proj_backend == "basemap"
+
+
+def test_proj_basemap_instance_deprecated():
+    pytest.importorskip("mpl_toolkits.basemap")
+    with pytest.warns(UltraPlotWarning, match="basemap backend was deprecated"):
+        basemap_proj = constructor.Proj("npstere", backend="basemap")
+        proj = constructor.Proj(basemap_proj)
+    assert proj is basemap_proj
+    assert proj._proj_backend == "basemap"
+
+
+def test_proj_basemap_rc_backend_deprecated():
+    pytest.importorskip("mpl_toolkits.basemap")
+    with uplt.rc.context({"geo.backend": "basemap"}):
+        with pytest.warns(UltraPlotWarning, match="basemap backend was deprecated"):
+            proj = constructor.Proj("npstere")
+    assert proj._proj_backend == "basemap"
+
+
+def test_proj_cartopy_backend_no_warning():
+    pytest.importorskip("cartopy")
+    with warnings.catch_warnings():
+        warnings.simplefilter("error", UltraPlotWarning)
+        proj = constructor.Proj("npstere", backend="cartopy")
+    assert proj._proj_backend == "cartopy"

ultraplot/tests/test_subplot_manager.py

@@ -33,7 +33,7 @@ def test_gridspec_setter_accepts_ultraplot():
 
 def test_parse_backend_basemap_warns():
     """parse_backend emits a deprecation warning for basemap."""
-    with pytest.warns(match="basemap"):
+    with pytest.warns(match="basemap backend was deprecated"):
         SubplotManager.parse_backend(backend="basemap")
 
 
@@ -43,6 +43,25 @@ def test_parse_backend_passthrough():
     assert SubplotManager.parse_backend(backend=None) is None
 
 
+def test_subplots_basemap_backend_warns():
+    """Requesting the basemap backend emits a deprecation warning."""
+    pytest.importorskip("mpl_toolkits.basemap")
+    with pytest.warns(match="basemap backend was deprecated"):
+        fig, axs = uplt.subplots(proj="cyl", backend="basemap")
+    assert axs[0]._name == "basemap"
+    uplt.close(fig)
+
+
+def test_subplots_basemap_instance_warns():
+    """Passing a Basemap instance as proj emits a deprecation warning."""
+    pytest.importorskip("mpl_toolkits.basemap")
+    with pytest.warns(match="basemap backend was deprecated"):
+        proj = uplt.Proj("npstere", backend="basemap")
+        fig, axs = uplt.subplots(proj=proj)
+    assert axs[0]._name == "basemap"
+    uplt.close(fig)
+
+
 def test_add_subplot_integer_arg():
     """add_subplot(111) creates a single subplot."""
     fig = uplt.figure()