While a speedup of 1% is measurable, contexts aren't created that often,

Stefan Krah · Stefan Krah · commit 3c29fd007474 · 2017-01-09T13:53:32.000+01:00
so let's defer this until 3.7, 3.8, ... all have this new function.
diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
@@ -1194,13 +1194,13 @@ context_new(PyTypeObject *type, PyObject *args UNUSED, PyObject *kwds UNUSED)
         return NULL;
     }
 
-    self->traps = _PyObject_CallNoArg((PyObject *)PyDecSignalDict_Type);
+    self->traps = PyObject_CallObject((PyObject *)PyDecSignalDict_Type, NULL);
     if (self->traps == NULL) {
         self->flags = NULL;
         Py_DECREF(self);
         return NULL;
     }
-    self->flags = _PyObject_CallNoArg((PyObject *)PyDecSignalDict_Type);
+    self->flags = PyObject_CallObject((PyObject *)PyDecSignalDict_Type, NULL);
     if (self->flags == NULL) {
         Py_DECREF(self);
         return NULL;
@@ -1395,7 +1395,7 @@ ieee_context(PyObject *dummy UNUSED, PyObject *v)
         goto error;
     }
 
-    context = _PyObject_CallNoArg((PyObject *)&PyDecContext_Type);
+    context = PyObject_CallObject((PyObject *)&PyDecContext_Type, NULL);
     if (context == NULL) {
         return NULL;
     }
@@ -1417,7 +1417,7 @@ context_copy(PyObject *self, PyObject *args UNUSED)
 {
     PyObject *copy;
 
-    copy = _PyObject_CallNoArg((PyObject *)&PyDecContext_Type);
+    copy = PyObject_CallObject((PyObject *)&PyDecContext_Type, NULL);
     if (copy == NULL) {
         return NULL;
     }

Original file line number	Diff line number	Diff line change
`@@ -1194,13 +1194,13 @@ context_new(PyTypeObject type, PyObject args UNUSED, PyObject *kwds UNUSED)`
`1194`	`1194`	`return NULL;`
`1195`	`1195`	`}`
`1196`	`1196`
`1197`		`- self->traps = _PyObject_CallNoArg((PyObject *)PyDecSignalDict_Type);`
	`1197`	`+ self->traps = PyObject_CallObject((PyObject *)PyDecSignalDict_Type, NULL);`
`1198`	`1198`	`if (self->traps == NULL) {`
`1199`	`1199`	`self->flags = NULL;`
`1200`	`1200`	`Py_DECREF(self);`
`1201`	`1201`	`return NULL;`
`1202`	`1202`	`}`
`1203`		`- self->flags = _PyObject_CallNoArg((PyObject *)PyDecSignalDict_Type);`
	`1203`	`+ self->flags = PyObject_CallObject((PyObject *)PyDecSignalDict_Type, NULL);`
`1204`	`1204`	`if (self->flags == NULL) {`
`1205`	`1205`	`Py_DECREF(self);`
`1206`	`1206`	`return NULL;`
`@@ -1395,7 +1395,7 @@ ieee_context(PyObject dummy UNUSED, PyObject v)`
`1395`	`1395`	`goto error;`
`1396`	`1396`	`}`
`1397`	`1397`
`1398`		`- context = _PyObject_CallNoArg((PyObject *)&PyDecContext_Type);`
	`1398`	`+ context = PyObject_CallObject((PyObject *)&PyDecContext_Type, NULL);`
`1399`	`1399`	`if (context == NULL) {`
`1400`	`1400`	`return NULL;`
`1401`	`1401`	`}`
`@@ -1417,7 +1417,7 @@ context_copy(PyObject self, PyObject args UNUSED)`
`1417`	`1417`	`{`
`1418`	`1418`	`PyObject *copy;`
`1419`	`1419`
`1420`		`- copy = _PyObject_CallNoArg((PyObject *)&PyDecContext_Type);`
	`1420`	`+ copy = PyObject_CallObject((PyObject *)&PyDecContext_Type, NULL);`
`1421`	`1421`	`if (copy == NULL) {`
`1422`	`1422`	`return NULL;`
`1423`	`1423`	`}`