diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
index ec206b926a4d..2e519149527f 100644
--- a/lib/matplotlib/colors.py
+++ b/lib/matplotlib/colors.py
@@ -43,6 +43,7 @@
from collections.abc import Sized, Sequence
import copy
import functools
+import importlib
import inspect
import io
import itertools
@@ -1528,9 +1529,22 @@ def _make_norm_from_scale(scale_cls, base_norm_cls, bound_init_signature):
class Norm(base_norm_cls):
def __reduce__(self):
+ cls = type(self)
+ # If the class is toplevel-accessible, it is possible to directly
+ # pickle it "by name". This is required to support norm classes
+ # defined at a module's toplevel, as the inner base_norm_cls is
+ # otherwise unpicklable (as it gets shadowed by the generated norm
+ # class). If either import or attribute access fails, fall back to
+ # the general path.
+ try:
+ if cls is getattr(importlib.import_module(cls.__module__),
+ cls.__qualname__):
+ return (_create_empty_object_of_class, (cls,), vars(self))
+ except (ImportError, AttributeError):
+ pass
return (_picklable_norm_constructor,
(scale_cls, base_norm_cls, bound_init_signature),
- self.__dict__)
+ vars(self))
def __init__(self, *args, **kwargs):
ba = bound_init_signature.bind(*args, **kwargs)
@@ -1603,11 +1617,14 @@ def autoscale_None(self, A):
return Norm
-def _picklable_norm_constructor(*args):
- cls = _make_norm_from_scale(*args)
+def _create_empty_object_of_class(cls):
return cls.__new__(cls)
+def _picklable_norm_constructor(*args):
+ return _create_empty_object_of_class(_make_norm_from_scale(*args))
+
+
@make_norm_from_scale(
scale.FuncScale,
init=lambda functions, vmin=None, vmax=None, clip=False: None)
diff --git a/lib/matplotlib/tests/test_pickle.py b/lib/matplotlib/tests/test_pickle.py
index 7cd23ea5c0eb..f4e35fb19b87 100644
--- a/lib/matplotlib/tests/test_pickle.py
+++ b/lib/matplotlib/tests/test_pickle.py
@@ -221,6 +221,11 @@ def test_mpl_toolkits():
assert type(pickle.loads(pickle.dumps(ax))) == parasite_axes.HostAxes
+def test_standard_norm():
+ assert type(pickle.loads(pickle.dumps(mpl.colors.LogNorm()))) \
+ == mpl.colors.LogNorm
+
+
def test_dynamic_norm():
logit_norm_instance = mpl.colors.make_norm_from_scale(
mpl.scale.LogitScale, mpl.colors.Normalize)()
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