addressed review comments

Author: emmanuelle

Diff for: CHANGELOG.md

@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fixed special cases with `px.sunburst` and `px.treemap` with `path` input ([#2524](https://github.com/plotly/plotly.py/pull/2524))
+- Fixed bug in `hover_data` argument of `px` functions, when the column name is changed with labels and `hover_data` is a dictionary setting up a specific format for the hover data ([#2544](https://github.com/plotly/plotly.py/pull/2544)).
 
 ## [4.8.1] - 2020-05-28
 

Diff for: packages/python/plotly/plotly/express/_core.py

@@ -117,6 +117,10 @@ def get_label(args, column):
 
 
 def invert_label(args, column):
+    """Invert mapping.
+    Find key corresponding to value column in dict args["labels"].
+    Returns `column` if the value does not exist.
+    """
     reversed_labels = {value: key for (key, value) in args["labels"].items()}
     try:
         return reversed_labels[column]
@@ -442,6 +446,7 @@ def make_trace_kwargs(args, trace_spec, trace_data, mapping_labels, sizeref):
         mapping_labels_copy = OrderedDict(mapping_labels)
         if args["hover_data"] and isinstance(args["hover_data"], dict):
             for k, v in mapping_labels.items():
+                # We need to invert the mapping here
                 k_args = invert_label(args, k)
                 if k_args in args["hover_data"]:
                     if args["hover_data"][k_args][0]: