Improved error message when subscripting types that don't support it

For example, `fig.update_layout(width_x=1)` gives the following error
message:

TypeError: 'NoneType' object is not subscriptable

Invalid value received for the 'width' property of layout

    The 'width' property is a number and may be specified as:
      - An int or float in the interval [10, inf]

Property does not support subscripting:
width_x
~~~~~

because `fig.layout['width']` can't be subscripted (you can't do
`fig.layout['width']['x'] = 1`)

Author: nicholas-esterer

packages/python/plotly/plotly/basedatatypes.py

@@ -118,20 +118,34 @@ def _check_path_in_prop_tree(obj, path):
     if type(path) == type(tuple()):
         path = _remake_path_from_tuple(path)
     prop, prop_idcs = _str_to_dict_path_full(path)
+    prev_objs = []
     for i, p in enumerate(prop):
         arg = ""
+        prev_objs.append(obj)
         try:
             obj = obj[p]
         except (ValueError, KeyError, IndexError, TypeError) as e:
             arg = e.args[0]
             if obj is None:
                 # If obj doesn't support subscripting, state that and show the
                 # (valid) property that gives the object that doesn't support
-                # it.
+                # subscripting.
+                if i > 0:
+                    validator = prev_objs[i - 1]._get_validator(prop[i - 1])
+                    arg += """
+
+Invalid value received for the '{plotly_name}' property of {parent_name}
+
+{description}""".format(
+                        parent_name=validator.parent_name,
+                        plotly_name=validator.plotly_name,
+                        description=validator.description(),
+                    )
                 # In case i is 0, the best we can do is indicate the first
                 # property in the string as having caused the error
                 disp_i = max(i - 1, 0)
                 arg += """
+
 Property does not support subscripting:
 %s
 %s""" % (

packages/python/plotly/plotly/tests/test_core/test_errors/test_dict_path_errors.py

@@ -289,9 +289,18 @@ def test_describes_subscripting_error(some_fig):
         some_fig.update_traces(text_yo="hey")
     except TypeError as e:
         raised = True
+        print(e.args[0])
         e_substr = error_substr(
             e.args[0],
             """
+
+Invalid value received for the 'text' property of scatter
+
+    The 'text' property is a string and must be specified as:
+      - A string
+      - A number that will be converted to a string
+      - A tuple, list, or one-dimensional numpy array of the above
+
 Property does not support subscripting:
 text_yo
 ~~~~""",
@@ -328,6 +337,13 @@ def test_describes_subscripting_error(some_fig):
         e_substr = error_substr(
             e.args[0],
             """
+
+Invalid value received for the 'family' property of scatter.textfont
+
+    The 'family' property is a string and must be specified as:
+      - A non-empty string
+      - A tuple, list, or one-dimensional numpy array of the above
+
 Property does not support subscripting:
 textfont_family_yo
          ~~~~~~""",
@@ -345,3 +361,6 @@ def test_describes_subscripting_error(some_fig):
             and (e_substr == e_correct_substr)
         )
     assert raised
+
+
+test_describes_subscripting_error(some_fig())