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Fix pickling of globally available, dynamically generated norm classes. #22815

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Merged
merged 1 commit into from
Apr 10, 2022
Merged

Fix pickling of globally available, dynamically generated norm classes. #22815

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23 changes: 20 additions & 3 deletions lib/matplotlib/colors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@
from collections.abc import Sized, Sequence
import copy
import functools
import importlib
import inspect
import io
import itertools
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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)
Expand Down
5 changes: 5 additions & 0 deletions lib/matplotlib/tests/test_pickle.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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)()
Expand Down