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pep-567: More additions (#510) 

* Add Token.MISSING and Token.old_value
* Change the signature of PyContextVar_Reset
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Yury Selivanov 2017-12-13 12:25:17 -05:00 committed by GitHub
parent 3b59266d43
commit 75fe7fe8b8
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1 changed files with 16 additions and 8 deletions
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pep-0567.rst
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@ -160,8 +160,14 @@ restore the ``ContextVar`` to its previous value, or remove it from
the context if the variable was not set before. It can be created
only by calling ``ContextVar.set()``.
For debug and introspection purposes it has a read-only attribute
``Token.var`` pointing to the variable that created the token.
For debug and introspection purposes it has:
* a read-only attribute ``Token.var`` pointing to the variable
that created the token;
* a read-only attribute ``Token.old_value`` set to the value the
variable had before the ``set()`` call, or to ``Token.MISSING``
if the variable wasn't set before.
Having the ``ContextVar.set()`` method returning a ``Token`` object
and the ``ContextVar.reset(token)`` method, allows context variables
@ -286,7 +292,7 @@ C API
3. ``PyContextToken * PyContextVar_Set(PyContextVar *, PyObject *)``:
set the value of the variable in the current context.
4. ``PyContextVar_Reset(PyContextToken *)``:
4. ``PyContextVar_Reset(PyContextVar *, PyContextToken *)``:
reset the value of the context variable.
5. ``PyContext * PyContext_New()``: create a new empty context.
@ -414,7 +420,7 @@ points to a ``_ContextData`` object::
try:
old_value = data.get(self)
except KeyError:
old_value = _NO_VALUE
old_value = Token.MISSING
ts.context_data = data.set(self, value)
return Token(self, old_value)
@ -423,7 +429,7 @@ points to a ``_ContextData`` object::
if token._used:
return
if token._old_value is _NO_VALUE:
if token._old_value is Token.MISSING:
ts.context_data = data.delete(token._var)
else:
ts.context_data = data.set(token._var,
@ -434,6 +440,8 @@ points to a ``_ContextData`` object::
class Token:
MISSING = object()
def __init__(self, var, old_value):
self._var = var
self._old_value = old_value
@ -443,9 +451,9 @@ points to a ``_ContextData`` object::
def var(self):
return self._var
(The ``_NO_VALUE`` is an internal marker object that will not be
part of the public API.)
@property
def old_value(self):
return self._old_value
Implementation Notes