rejecting trans argument on scales with fixed trans

plotnine/scales/scale.py

@@ -718,8 +718,26 @@ def get_labels(self, breaks=None):
         return labels
 
 
+class scale_continuous_fixed_transformation(scale_continuous):
+    """Base class/mixin for scales that have one fixed transformation,
+    which may not be overwritten by the user
+    e.g. scale_x_log10
+    """
+
+    def __init__(self, *args, **kwargs):
+        if 'trans' in kwargs and kwargs['trans'] != self._trans:
+            name = self.__class__.__name__
+            xy = 'x' if '_x_' in name else 'y'
+            raise ValueError(("%s is fixed to transformation %s "
+                              "- use scale_%s_continuous instead") %
+                             (name,
+                              self._trans,
+                              xy))
+        super().__init__(*args, **kwargs)
+
+
 @document
-class scale_datetime(scale_continuous):
+class scale_datetime(scale_continuous_fixed_transformation):
     """
     Base class for all date/datetime scales
 
@@ -770,4 +788,4 @@ def __init__(self, **kwargs):
             minor_breaks_fmt = kwargs.pop('date_minor_breaks')
             kwargs['minor_breaks'] = date_breaks(minor_breaks_fmt)
 
-        scale_continuous.__init__(self, **kwargs)
+        super().__init__(**kwargs)

plotnine/scales/scale_xy.py

@@ -6,7 +6,8 @@
 from ..utils import identity, match, alias, array_kind
 from ..exceptions import PlotnineError
 from .range import RangeContinuous
-from .scale import scale_discrete, scale_continuous, scale_datetime
+from .scale import (scale_discrete, scale_continuous, scale_datetime,
+                    scale_continuous_fixed_transformation)
 
 
 # positions scales have a couple of differences (quirks) that
@@ -225,7 +226,9 @@ class scale_y_datetime(scale_datetime, scale_y_continuous):
 
 
 @document
-class scale_x_timedelta(scale_x_continuous):
+class scale_x_timedelta(
+        scale_continuous_fixed_transformation,
+        scale_x_continuous):
     """
     Continuous x position for timedelta data points
 
@@ -237,7 +240,9 @@ class scale_x_timedelta(scale_x_continuous):
 
 
 @document
-class scale_y_timedelta(scale_y_continuous):
+class scale_y_timedelta(
+        scale_continuous_fixed_transformation,
+        scale_y_continuous):
     """
     Continuous y position for timedelta data points
 
@@ -249,7 +254,9 @@ class scale_y_timedelta(scale_y_continuous):
 
 
 @document
-class scale_x_sqrt(scale_x_continuous):
+class scale_x_sqrt(
+        scale_continuous_fixed_transformation,
+        scale_x_continuous):
     """
     Continuous x position sqrt transformed scale
 
@@ -261,7 +268,9 @@ class scale_x_sqrt(scale_x_continuous):
 
 
 @document
-class scale_y_sqrt(scale_y_continuous):
+class scale_y_sqrt(
+        scale_continuous_fixed_transformation,
+        scale_y_continuous):
     """
     Continuous y position sqrt transformed scale
 
@@ -273,7 +282,9 @@ class scale_y_sqrt(scale_y_continuous):
 
 
 @document
-class scale_x_log10(scale_x_continuous):
+class scale_x_log10(
+        scale_continuous_fixed_transformation,
+        scale_x_continuous):
     """
     Continuous x position log10 transformed scale
 
@@ -285,7 +296,9 @@ class scale_x_log10(scale_x_continuous):
 
 
 @document
-class scale_y_log10(scale_y_continuous):
+class scale_y_log10(
+        scale_continuous_fixed_transformation,
+        scale_y_continuous):
     """
     Continuous y position log10 transformed scale
 
@@ -297,7 +310,9 @@ class scale_y_log10(scale_y_continuous):
 
 
 @document
-class scale_x_reverse(scale_x_continuous):
+class scale_x_reverse(
+        scale_continuous_fixed_transformation,
+        scale_x_continuous):
     """
     Continuous x position reverse transformed scale
 
@@ -309,7 +324,9 @@ class scale_x_reverse(scale_x_continuous):
 
 
 @document
-class scale_y_reverse(scale_y_continuous):
+class scale_y_reverse(
+        scale_continuous_fixed_transformation,
+        scale_y_continuous):
     """
     Continuous y position reverse transformed scale
 

plotnine/tests/test_scale_internals.py

@@ -536,3 +536,34 @@ def test_legend_ordering_added_scales():
          )
 
     assert p + _theme == 'legend_ordering_added_scales'
+
+
+def test_trans_scales_raise_on_passing_trans():
+    # superfluous, but ok
+    scale_xy.scale_x_log10(trans='log10')
+    scale_xy.scale_x_reverse(trans='reverse')
+    scale_xy.scale_x_datetime(trans='datetime')
+    scale_xy.scale_x_timedelta(trans='pd_timedelta')
+
+    with pytest.raises(ValueError):
+        scale_xy.scale_x_log10(trans='identity')
+    with pytest.raises(ValueError):
+        scale_xy.scale_x_reverse(trans='identity')
+    with pytest.raises(ValueError):
+        scale_xy.scale_x_datetime(trans='identity')
+    with pytest.raises(ValueError):
+        scale_xy.scale_x_timedelta(trans='identity')
+
+    scale_xy.scale_y_log10(trans='log10')
+    scale_xy.scale_y_reverse(trans='reverse')
+    scale_xy.scale_y_datetime(trans='datetime')
+    scale_xy.scale_y_timedelta(trans='pd_timedelta')
+
+    with pytest.raises(ValueError):
+        scale_xy.scale_y_log10(trans='identity')
+    with pytest.raises(ValueError):
+        scale_xy.scale_y_reverse(trans='identity')
+    with pytest.raises(ValueError):
+        scale_xy.scale_y_datetime(trans='identity')
+    with pytest.raises(ValueError):
+        scale_xy.scale_y_timedelta(trans='identity')