fixed skimage import (#1832)

packages/python/plotly/plotly/express/__init__.py

@@ -2,6 +2,16 @@
 `plotly_express` is a terse, consistent, high-level wrapper around `plotly` for rapid \
 data exploration and figure generation. See the gallery at https://plotly.github.io/plotly_express
 """
+from __future__ import absolute_import
+from plotly import optional_imports
+
+pd = optional_imports.get_module("pandas")
+if pd is None:
+    raise ImportError(
+        """\
+Plotly express requires pandas to be installed."""
+    )
+
 
 from ._chart_types import (  # noqa: F401
     scatter,

packages/python/plotly/plotly/figure_factory/__init__.py

@@ -24,18 +24,31 @@
 from plotly.figure_factory._scatterplot import create_scatterplotmatrix
 from plotly.figure_factory._streamline import create_streamline
 from plotly.figure_factory._table import create_table
-from plotly.figure_factory._ternary_contour import create_ternary_contour
 from plotly.figure_factory._trisurf import create_trisurf
 from plotly.figure_factory._violin import create_violin
 
 if optional_imports.get_module("pandas") is not None:
     from plotly.figure_factory._county_choropleth import create_choropleth
+else:
+
+    def create_choropleth(*args, **kwargs):
+        raise ImportError("Please install pandas to use `create_choropleth`")
+
+
+if optional_imports.get_module("skimage") is not None:
+    from plotly.figure_factory._ternary_contour import create_ternary_contour
+else:
+
+    def create_ternary_contour(*args, **kwargs):
+        raise ImportError("Please install scikit-image to use `create_ternary_contour`")
+
 
 __all__ = [
     "create_2d_density",
     "create_annotated_heatmap",
     "create_bullet",
     "create_candlestick",
+    "create_choropleth",
     "create_dendrogram",
     "create_distplot",
     "create_facet_grid",

packages/python/plotly/tox.ini

@@ -74,6 +74,7 @@ deps=
     optional: pillow==5.2.0
     optional: matplotlib==2.2.3
     optional: xarray==0.10.9
+    optional: pywavelets==1.0.3
     optional: scikit-image==0.14.4
 
 ; CORE ENVIRONMENTS