cleanup pkg_resources references

and cleanup tests eg pandas-dev#27517

pandas/plotting/_core.py

@@ -1769,7 +1769,7 @@ def _load_backend(backend: str) -> types.ModuleType:
     ----------
     backend : str
         The identifier for the backend. Either an entrypoint item registered
-        with pkg_resources, "matplotlib", or a module name.
+        with importlib.metadata, "matplotlib", or a module name.
 
     Returns
     -------

pandas/tests/plotting/test_backend.py

@@ -1,7 +1,6 @@
 import sys
 import types
 
-import pkg_resources
 import pytest
 
 import pandas.util._test_decorators as td
@@ -45,40 +44,28 @@ def test_backend_can_be_set_in_plot_call(monkeypatch, restore_backend):
     assert df.plot(backend="pandas_dummy_backend") == "used_dummy"
 
 
-@td.skip_if_no_mpl
-def test_register_entrypoint(restore_backend):
-
-    dist = pkg_resources.get_distribution("pandas")
-    if dist.module_path not in pandas.__file__:
-        # We are running from a non-installed pandas, and this test is invalid
-        pytest.skip("Testing a non-installed pandas")
-
-    mod = types.ModuleType("my_backend")
-    mod.plot = lambda *args, **kwargs: 1
+def test_register_entrypoint(restore_backend, tmp_path, monkeypatch):
+    monkeypatch.syspath_prepend(tmp_path)
+    monkeypatch.setitem(sys.modules, "pandas_dummy_backend", dummy_backend)
 
-    backends = pkg_resources.get_entry_map("pandas")
-    my_entrypoint = pkg_resources.EntryPoint(
-        "pandas_plotting_backend", mod.__name__, dist=dist
+    dist_info = tmp_path / "my_backend-0.0.0.dist-info"
+    dist_info.mkdir()
+    # entry_point name should not match module name - otherwise pandas will
+    # fall back to backend lookup by module name
+    (dist_info / "entry_points.txt").write_bytes(
+        b"[pandas_plotting_backend]\nmy_ep_backend = pandas_dummy_backend\n"
     )
-    backends["pandas_plotting_backends"]["my_backend"] = my_entrypoint
-    # TODO: the docs recommend importlib.util.module_from_spec. But this works for now.
-    sys.modules["my_backend"] = mod
-
-    result = pandas.plotting._core._get_plot_backend("my_backend")
-    assert result is mod
 
-    # TODO(GH#27517): https://github.com/pandas-dev/pandas/issues/27517
-    # Remove the td.skip_if_no_mpl
-    with pandas.option_context("plotting.backend", "my_backend"):
-        result = pandas.plotting._core._get_plot_backend()
+    assert pandas.plotting._core._get_plot_backend("my_ep_backend") is dummy_backend
 
-    assert result is mod
+    with pandas.option_context("plotting.backend", "my_ep_backend"):
+        assert pandas.plotting._core._get_plot_backend() is dummy_backend
 
 
-def test_setting_backend_without_plot_raises():
+def test_setting_backend_without_plot_raises(monkeypatch):
     # GH-28163
     module = types.ModuleType("pandas_plot_backend")
-    sys.modules["pandas_plot_backend"] = module
+    monkeypatch.setitem(sys.modules, "pandas_plot_backend", module)
 
     assert pandas.options.plotting.backend == "matplotlib"
     with pytest.raises(