Speedup normalize_kwargs by storing aliases in a more practical format.

Directly store property alias information in `{"alias": "propety", ...}` format, which greatly speeds up normalize_kwargs. In order to not worry about two different dict formats (the new one, and the old one, which was `{"property": ["alias", ...], ...}`) in normalize_kwargs, deprecate support for directly passing an alias map -- callers should always pass an artist (or artist type) directly, which hides the detail of the format of the alias map. Also deprecate passing `alias_mapping=None`, which doesn't really seem needed (unlike `kw=None`, which is regularly used). Whether the format of aliases passed to `_api.define_aliases` should also be changed to match the new format is a separate question that doesn't have to be addressed here (it can be changed later, being fully private anyways).
llohse · Jan 19, 2026 · Jan 20, 2026 · Jan 22, 2026 · Jan 21, 2026 · Dec 1, 2025
commit 9387f36f14573827250a05e6864c1b1e204d5b7e
diff --git a/doc/api/next_api_changes/deprecations/31023-AL.rst b/doc/api/next_api_changes/deprecations/31023-AL.rst
@@ -0,0 +1,4 @@
+``cbook.normalize_kwargs`` only supports passing artists and artist classes as second argument
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Support for directly passing an alias mapping or None as second argument to
+`.cbook.normalize_kwargs` has been deprecated.
diff --git a/lib/matplotlib/_api/__init__.py b/lib/matplotlib/_api/__init__.py
@@ -269,8 +269,9 @@ class so far, an alias named ``get_alias`` will be defined; the same will
     be done for setters.  If neither the getter nor the setter exists, an
     exception will be raised.
 
-    The alias map is stored as the ``_alias_map`` attribute on the class and
-    can be used by `.normalize_kwargs`.
+    The alias map is stored as the ``_alias_to_prop`` attribute under the format
+    ``{"alias": "property", ...}` on the class, and can be used by
+    `.normalize_kwargs`.
     """
     if cls is None:  # Return the actual class decorator.
         return functools.partial(define_aliases, alias_d)
@@ -295,17 +296,20 @@ def method(self, *args, **kwargs):
             raise ValueError(
                 f"Neither getter nor setter exists for {prop!r}")
 
+    alias_to_prop = {
+        alias: prop for prop, aliases in alias_d.items() for alias in aliases}
+
     def get_aliased_and_aliases(d):
-        return {*d, *(alias for aliases in d.values() for alias in aliases)}
+        return {*d.keys(), *d.values()}
 
-    preexisting_aliases = getattr(cls, "_alias_map", {})
+    preexisting_aliases = getattr(cls, "_alias_to_prop", {})
     conflicting = (get_aliased_and_aliases(preexisting_aliases)
-                   & get_aliased_and_aliases(alias_d))
+                   & get_aliased_and_aliases(alias_to_prop))
     if conflicting:
         # Need to decide on conflict resolution policy.
         raise NotImplementedError(
             f"Parent class already defines conflicting aliases: {conflicting}")
-    cls._alias_map = {**preexisting_aliases, **alias_d}
+    cls._alias_to_prop = {**preexisting_aliases, **alias_to_prop}
     return cls
 
 

diff --git a/lib/matplotlib/cbook.py b/lib/matplotlib/cbook.py
@@ -1831,7 +1831,7 @@ def normalize_kwargs(kw, alias_mapping=None):
         as an empty dict, to support functions with an optional parameter of
         the form ``props=None``.
 
-    alias_mapping : dict or Artist subclass or Artist instance, optional
+    alias_mapping : Artist subclass or Artist instance
         A mapping between a canonical name to a list of aliases, in order of
         precedence from lowest to highest.
 
@@ -1849,31 +1849,35 @@ def normalize_kwargs(kw, alias_mapping=None):
     """
     from matplotlib.artist import Artist
 
+    # deal with default value of alias_mapping
+    if (isinstance(alias_mapping, type) and issubclass(alias_mapping, Artist)
+          or isinstance(alias_mapping, Artist)):
+        alias_to_prop = getattr(alias_mapping, "_alias_to_prop", {})
+    else:
+        if alias_mapping is None:
+            alias_mapping = {}
+        _api.warn_deprecated("3.11", message=(
+            "Passing a dict or None as alias_mapping to normalize_kwargs is "
+            "deprecated since %(since)s and support will be removed "
+            "%(removal)s; pass an Artist instance or type instead."))
+        # Convert old format to new format.
+        alias_to_prop = {alias: prop for prop, aliases in alias_mapping.items()
+                         for alias in aliases}
+
     if kw is None:
         return {}
 
-    # deal with default value of alias_mapping
-    if alias_mapping is None:
-        alias_mapping = {}
-    elif (isinstance(alias_mapping, type) and issubclass(alias_mapping, Artist)
-          or isinstance(alias_mapping, Artist)):
-        alias_mapping = getattr(alias_mapping, "_alias_map", {})
+    canonicalized = {alias_to_prop.get(k, k): v for k, v in kw.items()}
+    if len(canonicalized) == len(kw):
+        return canonicalized
 
-    to_canonical = {alias: canonical
-                    for canonical, alias_list in alias_mapping.items()
-                    for alias in alias_list}
     canonical_to_seen = {}
-    ret = {}  # output dictionary
-
-    for k, v in kw.items():
-        canonical = to_canonical.get(k, k)
+    for k in kw:
+        canonical = alias_to_prop.get(k, k)
         if canonical in canonical_to_seen:
             raise TypeError(f"Got both {canonical_to_seen[canonical]!r} and "
                             f"{k!r}, which are aliases of one another")
         canonical_to_seen[canonical] = k
-        ret[canonical] = v
-
-    return ret
 
 
 @contextlib.contextmanager

diff --git a/lib/matplotlib/cbook.pyi b/lib/matplotlib/cbook.pyi
@@ -150,7 +150,7 @@ def sanitize_sequence(data): ...
 def _resize_sequence(seq: Sequence, N: int) -> Sequence: ...
 def normalize_kwargs(
     kw: dict[str, Any],
-    alias_mapping: dict[str, list[str]] | type[Artist] | Artist | None = ...,
+    alias_mapping: type[Artist] | Artist | None = ...,
 ) -> dict[str, Any]: ...
 def _lock_path(path: str | os.PathLike) -> contextlib.AbstractContextManager[None]: ...
 def _str_equal(obj: Any, s: str) -> bool: ...

diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
@@ -15,6 +15,7 @@
                            assert_array_almost_equal)
 import pytest
 
+import matplotlib as mpl
 from matplotlib import _api, cbook
 import matplotlib.colors as mcolors
 from matplotlib.cbook import delete_masked_points, strip_math
@@ -480,30 +481,42 @@ def test_resize_sequence():
     assert_array_equal(cbook._resize_sequence(arr, 5), [1, 2, 3, 1, 2])
 
 
-fail_mapping: tuple[tuple[dict, dict], ...] = (
-    ({'a': 1, 'b': 2}, {'alias_mapping': {'a': ['b']}}),
-    ({'a': 1, 'b': 2}, {'alias_mapping': {'a': ['a', 'b']}}),
-)
+fail_mapping: list[tuple[dict, dict]] = [
+    ({"a": 1, "b": 2}, {"a": ["b"]}),
+    ({"a": 1, "b": 2}, {"a": ["a", "b"]}),
+]
 
-pass_mapping: tuple[tuple[Any, dict, dict], ...] = (
+pass_mapping: list[tuple[Any, dict, dict]] = [
     (None, {}, {}),
-    ({'a': 1, 'b': 2}, {'a': 1, 'b': 2}, {}),
-    ({'b': 2}, {'a': 2}, {'alias_mapping': {'a': ['a', 'b']}}),
-)
+    ({"a": 1, "b": 2}, {"a": 1, "b": 2}, {}),
+    ({"b": 2}, {"a": 2}, {"a": ["a", "b"]}),
+]
 
 
-@pytest.mark.parametrize('inp, kwargs_to_norm', fail_mapping)
-def test_normalize_kwargs_fail(inp, kwargs_to_norm):
-    with pytest.raises(TypeError), _api.suppress_matplotlib_deprecation_warning():
-        cbook.normalize_kwargs(inp, **kwargs_to_norm)
+@pytest.mark.parametrize('inp, alias_def', fail_mapping)
+def test_normalize_kwargs_fail(inp, alias_def):
 
+    @_api.define_aliases(alias_def)
+    class Type(mpl.artist.Artist):
+        def get_a(self): return None
 
-@pytest.mark.parametrize('inp, expected, kwargs_to_norm',
-                         pass_mapping)
-def test_normalize_kwargs_pass(inp, expected, kwargs_to_norm):
-    with _api.suppress_matplotlib_deprecation_warning():
-        # No other warning should be emitted.
-        assert expected == cbook.normalize_kwargs(inp, **kwargs_to_norm)
+    with pytest.raises(TypeError):
+        cbook.normalize_kwargs(inp, Type)
+
+
+@pytest.mark.parametrize('inp, expected, alias_def', pass_mapping)
+def test_normalize_kwargs_pass(inp, expected, alias_def):
+
+    @_api.define_aliases(alias_def)
+    class Type(mpl.artist.Artist):
+        def get_a(self): return None
+
+    assert expected == cbook.normalize_kwargs(inp, Type)
+    old_alias_map = {}
+    for alias, prop in Type._alias_to_prop.items():
+        old_alias_map.setdefault(prop, []).append(alias)
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        assert expected == cbook.normalize_kwargs(inp, old_alias_map)
 
 
 def test_warn_external(recwarn):

diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -3089,7 +3089,7 @@ def __init__(self, ax, x, y, *, marker='o', marker_props=None, useblit=True):
         props = {'marker': marker, 'markersize': 7, 'markerfacecolor': 'w',
                  'linestyle': 'none', 'alpha': 0.5, 'visible': False,
                  'label': '_nolegend_',
-                 **cbook.normalize_kwargs(marker_props, Line2D._alias_map)}
+                 **cbook.normalize_kwargs(marker_props, Line2D)}
         self._markers = Line2D(x, y, animated=useblit, **props)
         self.ax.add_line(self._markers)