Show the right style options with the help function (#754)

.gitignore

@@ -45,6 +45,7 @@ nosetests.xml
 coverage.xml
 *.cover
 .hypothesis/
+.pytest_cache
 
 # Translations
 *.mo

hvplot/__init__.py

@@ -42,7 +42,7 @@ def _get_doc_and_signature(
         formatter += "{options}"
 
     # Bokeh is the default backend
-    backend = hvplot_extension.compatibility or 'bokeh'
+    backend = hvplot_extension.compatibility or Store.current_backend
     if eltype in Store.registry[backend]:
         valid_opts = Store.registry[backend][eltype].style_opts
         if style:

hvplot/tests/testhelp.py

@@ -0,0 +1,66 @@
+import hvplot.pandas
+import pytest
+
+from holoviews.core import Store
+from holoviews.element import Curve
+
+
+@pytest.fixture
+def reset_default_backend():
+    yield
+    hvplot.extension('bokeh')
+    hvplot.extension.compatibility = None
+
+
+def test_help_style_extension_output(reset_default_backend):
+    # default, after e.g. import hvplot.pandas
+    docstring, signature = hvplot._get_doc_and_signature(
+        cls=hvplot.hvPlot,
+        kind='line',
+        completions=False,
+        docstring=False,
+        generic=False,
+        style=True,
+        signature=None,
+    )
+    assert docstring == '\nStyle options\n-------------\n\n' + '\n'.join(sorted(Store.registry['bokeh'][Curve].style_opts))
+
+    # The current backend becomes matplotlib
+    hvplot.extension('matplotlib', 'plotly')
+    docstring, signature = hvplot._get_doc_and_signature(
+        cls=hvplot.hvPlot,
+        kind='line',
+        completions=False,
+        docstring=False,
+        generic=False,
+        style=True,
+        signature=None,
+    )
+    assert docstring == '\nStyle options\n-------------\n\n' + '\n'.join(sorted(Store.registry['matplotlib'][Curve].style_opts))
+
+    # The current backend becomes plotly
+    hvplot.output(backend='plotly')
+    docstring, signature = hvplot._get_doc_and_signature(
+        cls=hvplot.hvPlot,
+        kind='line',
+        completions=False,
+        docstring=False,
+        generic=False,
+        style=True,
+        signature=None,
+    )
+    assert docstring == '\nStyle options\n-------------\n\n' + '\n'.join(sorted(Store.registry['plotly'][Curve].style_opts))
+
+def test_help_style_compatibility(reset_default_backend):
+    # The current backend is plotly but the style options are those of matplotlib
+    hvplot.extension('plotly', 'matplotlib', compatibility='matplotlib')
+    docstring, signature = hvplot._get_doc_and_signature(
+        cls=hvplot.hvPlot,
+        kind='line',
+        completions=False,
+        docstring=False,
+        generic=False,
+        style=True,
+        signature=None,
+    )
+    assert docstring == '\nStyle options\n-------------\n\n' + '\n'.join(sorted(Store.registry['matplotlib'][Curve].style_opts))