px.Constant

Author: nicolaskruchten

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

@@ -54,6 +54,7 @@
     defaults,
     get_trendline_results,
     IdentityMap,
+    Constant,
 )
 
 from . import data, colors  # noqa: F401
@@ -97,4 +98,5 @@
     "set_mapbox_access_token",
     "get_trendline_results",
     "IdentityMap",
+    "Constant",
 ]

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

@@ -59,6 +59,12 @@ def copy(self):
         return self
 
 
+class Constant(object):
+    def __init__(self, value, label=None):
+        self.value = value
+        self.label = label
+
+
 MAPBOX_TOKEN = None
 
 
@@ -937,6 +943,8 @@ def build_dataframe(args, attrables, array_attrables):
         else:
             df_output[df_input.columns] = df_input[df_input.columns]
 
+    constants = dict()
+
     # Loop over possible arguments
     for field_name in attrables:
         # Massaging variables
@@ -968,8 +976,15 @@ def build_dataframe(args, attrables, array_attrables):
                     "pandas MultiIndex is not supported by plotly express "
                     "at the moment." % field
                 )
+            # ----------------- argument is a constant ----------------------
+            if isinstance(argument, Constant):
+                col_name = _check_name_not_reserved(
+                    str(argument.label) if argument.label is not None else field,
+                    reserved_names,
+                )
+                constants[col_name] = argument.value
             # ----------------- argument is a col name ----------------------
-            if isinstance(argument, str) or isinstance(
+            elif isinstance(argument, str) or isinstance(
                 argument, int
             ):  # just a column name given as str or int
                 if not df_provided:
@@ -1050,6 +1065,9 @@ def build_dataframe(args, attrables, array_attrables):
             else:
                 args[field_name][i] = str(col_name)
 
+    for col_name in constants:
+        df_output[col_name] = constants[col_name]
+
     args["data_frame"] = df_output
     return args
 

Diff for: packages/python/plotly/plotly/tests/test_core/test_px/test_px_input.py

@@ -335,6 +335,36 @@ def test_identity_map():
     )
     assert fig.data[0].marker.color == "red"
     assert fig.data[1].marker.color == "blue"
-    assert "color" not in fig.data[0].hovertemplate
-    assert "symbol" in fig.data[0].hovertemplate
+    assert "color=" not in fig.data[0].hovertemplate
+    assert "symbol=" in fig.data[0].hovertemplate
+    assert fig.layout.legend.title.text == "symbol"
+
+
+def test_constants():
+    fig = px.scatter(x=px.Constant(1), y=[1, 2])
+    assert fig.data[0].x[0] == 1
+    assert fig.data[0].x[1] == 1
+    assert "x=" in fig.data[0].hovertemplate
+
+    fig = px.scatter(x=px.Constant(1, label="time"), y=[1, 2])
+    assert fig.data[0].x[0] == 1
+    assert fig.data[0].x[1] == 1
+    assert "x=" not in fig.data[0].hovertemplate
+    assert "time=" in fig.data[0].hovertemplate
+
+    fig = px.scatter(
+        x=[1, 2],
+        y=[1, 2],
+        symbol=["a", "b"],
+        color=px.Constant("red", label="the_identity_label"),
+        hover_data=[px.Constant("data", label="the_data")],
+        color_discrete_map=px.IdentityMap(),
+    )
+    assert fig.data[0].marker.color == "red"
+    assert fig.data[0].customdata[0][0] == "data"
+    assert fig.data[1].marker.color == "red"
+    assert "color=" not in fig.data[0].hovertemplate
+    assert "the_identity_label=" not in fig.data[0].hovertemplate
+    assert "symbol=" in fig.data[0].hovertemplate
+    assert "the_data=" in fig.data[0].hovertemplate
     assert fig.layout.legend.title.text == "symbol"