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Commit469d2e4

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gh-129889: Support context manager protocol by contextvars.Token (#129888)
1 parente1b38ea commit469d2e4

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6 files changed

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6 files changed

+223
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lines changed

‎Doc/library/contextvars.rst‎

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Original file line numberDiff line numberDiff line change
@@ -101,6 +101,21 @@ Context Variables
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the value of the variable to what it was before the corresponding
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*set*.
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The token supports:ref:`context manager protocol<context-managers>`
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to restore the corresponding context variable value at the exit from
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:keyword:`with` block::
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var = ContextVar('var', default='default value')
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with var.set('new value'):
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assert var.get() == 'new value'
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assert var.get() == 'default value'
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..versionadded::next
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Added support for usage as a context manager.
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..attribute::Token.var
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A read-only property. Points to the:class:`ContextVar` object

‎Doc/whatsnew/3.14.rst‎

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@@ -1,4 +1,3 @@
1-
21
****************************
32
What's new in Python 3.14
43
****************************
@@ -362,6 +361,13 @@ concurrent.futures
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supplying a *mp_context* to:class:`concurrent.futures.ProcessPoolExecutor`.
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(Contributed by Gregory P. Smith in:gh:`84559`.)
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contextvars
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-----------
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* Support context manager protocol by:class:`contextvars.Token`.
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(Contributed by Andrew Svetlov in:gh:`129889`.)
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365371
ctypes
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------
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‎Lib/test/test_context.py‎

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Original file line numberDiff line numberDiff line change
@@ -383,6 +383,115 @@ def sub(num):
383383
tp.shutdown()
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self.assertEqual(results,list(range(10)))
385385

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deftest_token_contextmanager_with_default(self):
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ctx=contextvars.Context()
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c=contextvars.ContextVar('c',default=42)
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deffun():
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withc.set(36):
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self.assertEqual(c.get(),36)
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self.assertEqual(c.get(),42)
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ctx.run(fun)
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deftest_token_contextmanager_without_default(self):
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ctx=contextvars.Context()
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c=contextvars.ContextVar('c')
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deffun():
403+
withc.set(36):
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self.assertEqual(c.get(),36)
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withself.assertRaisesRegex(LookupError,"<ContextVar name='c'"):
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c.get()
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ctx.run(fun)
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deftest_token_contextmanager_on_exception(self):
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ctx=contextvars.Context()
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c=contextvars.ContextVar('c',default=42)
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deffun():
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withc.set(36):
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self.assertEqual(c.get(),36)
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raiseValueError("custom exception")
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self.assertEqual(c.get(),42)
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withself.assertRaisesRegex(ValueError,"custom exception"):
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ctx.run(fun)
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deftest_token_contextmanager_reentrant(self):
426+
ctx=contextvars.Context()
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c=contextvars.ContextVar('c',default=42)
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deffun():
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token=c.set(36)
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withself.assertRaisesRegex(
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RuntimeError,
433+
"<Token .+ has already been used once"
434+
):
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withtoken:
436+
withtoken:
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self.assertEqual(c.get(),36)
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self.assertEqual(c.get(),42)
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ctx.run(fun)
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deftest_token_contextmanager_multiple_c_set(self):
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ctx=contextvars.Context()
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c=contextvars.ContextVar('c',default=42)
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deffun():
448+
withc.set(36):
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self.assertEqual(c.get(),36)
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c.set(24)
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self.assertEqual(c.get(),24)
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c.set(12)
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self.assertEqual(c.get(),12)
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self.assertEqual(c.get(),42)
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ctx.run(fun)
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deftest_token_contextmanager_with_explicit_reset_the_same_token(self):
460+
ctx=contextvars.Context()
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c=contextvars.ContextVar('c',default=42)
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deffun():
464+
withself.assertRaisesRegex(
465+
RuntimeError,
466+
"<Token .+ has already been used once"
467+
):
468+
withc.set(36)astoken:
469+
self.assertEqual(c.get(),36)
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c.reset(token)
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self.assertEqual(c.get(),42)
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self.assertEqual(c.get(),42)
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ctx.run(fun)
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deftest_token_contextmanager_with_explicit_reset_another_token(self):
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ctx=contextvars.Context()
480+
c=contextvars.ContextVar('c',default=42)
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482+
deffun():
483+
withc.set(36):
484+
self.assertEqual(c.get(),36)
485+
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token=c.set(24)
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self.assertEqual(c.get(),24)
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c.reset(token)
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self.assertEqual(c.get(),36)
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self.assertEqual(c.get(),42)
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ctx.run(fun)
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386495

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# HAMT Tests
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@@ -0,0 +1,2 @@
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Support context manager protocol by:class:`contextvars.Token`. Patch by
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Andrew Svetlov.

‎Python/clinic/context.c.h‎

Lines changed: 52 additions & 1 deletion
Some generated files are not rendered by default. Learn more aboutcustomizing how changed files appear on GitHub.

‎Python/context.c‎

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Original file line numberDiff line numberDiff line change
@@ -1231,9 +1231,47 @@ static PyGetSetDef PyContextTokenType_getsetlist[] = {
12311231
{NULL}
12321232
};
12331233

1234+
/*[clinic input]
1235+
_contextvars.Token.__enter__ as token_enter
1236+
1237+
Enter into Token context manager.
1238+
[clinic start generated code]*/
1239+
1240+
staticPyObject*
1241+
token_enter_impl(PyContextToken*self)
1242+
/*[clinic end generated code: output=9af4d2054e93fb75 input=41a3d6c4195fd47a]*/
1243+
{
1244+
returnPy_NewRef(self);
1245+
}
1246+
1247+
/*[clinic input]
1248+
_contextvars.Token.__exit__ as token_exit
1249+
1250+
type: object
1251+
val: object
1252+
tb: object
1253+
/
1254+
1255+
Exit from Token context manager, restore the linked ContextVar.
1256+
[clinic start generated code]*/
1257+
1258+
staticPyObject*
1259+
token_exit_impl(PyContextToken*self,PyObject*type,PyObject*val,
1260+
PyObject*tb)
1261+
/*[clinic end generated code: output=3e6a1c95d3da703a input=7f117445f0ccd92e]*/
1262+
{
1263+
intret=PyContextVar_Reset((PyObject*)self->tok_var, (PyObject*)self);
1264+
if (ret<0) {
1265+
returnNULL;
1266+
}
1267+
Py_RETURN_NONE;
1268+
}
1269+
12341270
staticPyMethodDefPyContextTokenType_methods[]= {
12351271
{"__class_getitem__",Py_GenericAlias,
12361272
METH_O|METH_CLASS,PyDoc_STR("See PEP 585")},
1273+
TOKEN_ENTER_METHODDEF
1274+
TOKEN_EXIT_METHODDEF
12371275
{NULL}
12381276
};
12391277

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