Remove need for ConversionInterface to support unitless values.

This avoids having each ConversionInterface.convert having to start by
doing the same call to is_numlike.

(Axis.convert_units, which should be the user-facing entry point, checks
_is_natively_supported first, which prevents unitless values from being
sent to ConversionInterface.convert.)

Author: anntzer

doc/api/next_api_changes/deprecations/20334-AL.rst

@@ -0,0 +1,11 @@
+``ConversionInterface.convert`` no longer needs to accept unitless values
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Previously, custom subclasses of `.units.ConversionInterface` needed to
+implement a ``convert`` method that not only accepted instances of the
+unit, but also unitless values (which are passed through as is).  This is
+no longer the case (``convert`` is never called with a unitless value),
+and such support in `.StrCategoryConverter` is deprecated.  Likewise, the
+`.ConversionInterface.is_numlike` helper is deprecated.
+
+Consider calling `.Axis.convert_units` instead, which still supports unitless
+values.

examples/units/basic_units.py

@@ -343,8 +343,6 @@ def axisinfo(unit, axis):
 
     @staticmethod
     def convert(val, unit, axis):
-        if units.ConversionInterface.is_numlike(val):
-            return val
         if np.iterable(val):
             if isinstance(val, np.ma.MaskedArray):
                 val = val.astype(float).filled(np.nan)

examples/units/evans_test.py

@@ -48,9 +48,6 @@ def convert(obj, unit, axis):
 
         If *obj* is a sequence, return the converted sequence.
         """
-        if units.ConversionInterface.is_numlike(obj):
-            return obj
-
         if np.iterable(obj):
             return [o.value(unit) for o in obj]
         else:

lib/matplotlib/axis.py

@@ -2273,9 +2273,7 @@ def set_default_intervals(self):
             if self.converter is not None:
                 info = self.converter.axisinfo(self.units, self)
                 if info.default_limits is not None:
-                    valmin, valmax = info.default_limits
-                    xmin = self.converter.convert(valmin, self.units, self)
-                    xmax = self.converter.convert(valmax, self.units, self)
+                    xmin, xmax = self.convert_units(info.default_limits)
             if not dataMutated:
                 self.axes.dataLim.intervalx = xmin, xmax
             if not viewMutated:
@@ -2538,9 +2536,7 @@ def set_default_intervals(self):
             if self.converter is not None:
                 info = self.converter.axisinfo(self.units, self)
                 if info.default_limits is not None:
-                    valmin, valmax = info.default_limits
-                    ymin = self.converter.convert(valmin, self.units, self)
-                    ymax = self.converter.convert(valmax, self.units, self)
+                    ymin, ymax = self.convert_units(info.default_limits)
             if not dataMutated:
                 self.axes.dataLim.intervaly = ymin, ymax
             if not viewMutated:

lib/matplotlib/category.py

@@ -54,9 +54,15 @@ def convert(value, unit, axis):
         # dtype = object preserves numerical pass throughs
         values = np.atleast_1d(np.array(value, dtype=object))
         # pass through sequence of non binary numbers
-        if all(units.ConversionInterface.is_numlike(v)
-               and not isinstance(v, (str, bytes))
-               for v in values):
+        with _api.suppress_matplotlib_deprecation_warning():
+            is_numlike = all(units.ConversionInterface.is_numlike(v)
+                             and not isinstance(v, (str, bytes))
+                             for v in values)
+        if is_numlike:
+            _api.warn_deprecated(
+                "3.5", message="Support for passing numbers through unit "
+                "converters is deprecated since %(since)s and support will be "
+                "removed %(removal)s; use Axis.convert_units instead.")
             return np.asarray(values, dtype=float)
         # force an update so it also does type checking
         unit.update(values)

lib/matplotlib/testing/jpl_units/EpochConverter.py

@@ -81,8 +81,6 @@ def convert(value, unit, axis):
 
         if not cbook.is_scalar_or_string(value):
             return [EpochConverter.convert(x, unit, axis) for x in value]
-        if units.ConversionInterface.is_numlike(value):
-            return value
         if unit is None:
             unit = EpochConverter.default_units(value, axis)
         if isinstance(value, U.Duration):

lib/matplotlib/testing/jpl_units/StrConverter.py

@@ -27,9 +27,6 @@ def axisinfo(unit, axis):
     def convert(value, unit, axis):
         # docstring inherited
 
-        if units.ConversionInterface.is_numlike(value):
-            return value
-
         if value == []:
             return []
 

lib/matplotlib/testing/jpl_units/UnitDblConverter.py

@@ -66,11 +66,6 @@ def convert(value, unit, axis):
         # docstring inherited
         if not cbook.is_scalar_or_string(value):
             return [UnitDblConverter.convert(x, unit, axis) for x in value]
-        # If the incoming value behaves like a number,
-        # then just return it because we don't know how to convert it
-        # (or it is already converted)
-        if units.ConversionInterface.is_numlike(value):
-            return value
         # If no units were specified, then get the default units to use.
         if unit is None:
             unit = UnitDblConverter.default_units(value, axis)

lib/matplotlib/tests/test_category.py

@@ -2,6 +2,7 @@
 import pytest
 import numpy as np
 
+from matplotlib._api import MatplotlibDeprecationWarning
 from matplotlib.axes import Axes
 import matplotlib.pyplot as plt
 import matplotlib.category as cat
@@ -100,12 +101,14 @@ def test_convert_one_string(self, value):
         assert self.cc.convert(value, self.unit, self.ax) == 0
 
     def test_convert_one_number(self):
-        actual = self.cc.convert(0.0, self.unit, self.ax)
+        with pytest.warns(MatplotlibDeprecationWarning):
+            actual = self.cc.convert(0.0, self.unit, self.ax)
         np.testing.assert_allclose(actual, np.array([0.]))
 
     def test_convert_float_array(self):
         data = np.array([1, 2, 3], dtype=float)
-        actual = self.cc.convert(data, self.unit, self.ax)
+        with pytest.warns(MatplotlibDeprecationWarning):
+            actual = self.cc.convert(data, self.unit, self.ax)
         np.testing.assert_allclose(actual, np.array([1., 2., 3.]))
 
     @pytest.mark.parametrize("fvals", fvalues, ids=fids)

lib/matplotlib/units.py

@@ -48,7 +48,7 @@ def default_units(x, axis):
 import numpy as np
 from numpy import ma
 
-from matplotlib import cbook
+from matplotlib import _api, cbook
 
 
 class ConversionError(TypeError):
@@ -134,6 +134,7 @@ def convert(obj, unit, axis):
         return obj
 
     @staticmethod
+    @_api.deprecated("3.5")
     def is_numlike(x):
         """
         The Matplotlib datalim, autoscaling, locators etc work with scalars