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Simplify CallbackRegistry pickling. #16219

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Mar 9, 2020
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Simplify CallbackRegistry pickling. #16219

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19 changes: 4 additions & 15 deletions lib/matplotlib/cbook/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -151,29 +151,18 @@ def h(exc):
"""

# We maintain two mappings:
# callbacks: signal -> {cid -> callback}
# _func_cid_map: signal -> {callback -> cid}
# (actually, callbacks are weakrefs to the actual callbacks).
# callbacks: signal -> {cid -> weakref-to-callback}
# _func_cid_map: signal -> {weakref-to-callback -> cid}

def __init__(self, exception_handler=_exception_printer):
self.exception_handler = exception_handler
self.callbacks = {}
self._cid_gen = itertools.count()
self._func_cid_map = {}

# In general, callbacks may not be pickled; thus, we simply recreate an
# empty dictionary at unpickling. In order to ensure that `__setstate__`
# (which just defers to `__init__`) is called, `__getstate__` must
# return a truthy value (for pickle protocol>=3, i.e. Py3, the
# *actual* behavior is that `__setstate__` will be called as long as
# `__getstate__` does not return `None`, but this is undocumented -- see
# http://bugs.python.org/issue12290).

def __getstate__(self):
return {'exception_handler': self.exception_handler}

def __setstate__(self, state):
self.__init__(**state)
# In general, callbacks may not be pickled, so we just drop them.
return {**vars(self), "callbacks": {}, "_func_cid_map": {}}

def connect(self, s, func):
"""Register *func* to be called when signal *s* is generated.
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