gh-91576: Speed up iteration of strings (#91574)

Author: kumaraditya303

Include/internal/pycore_unicodeobject.h

@@ -20,6 +20,7 @@ extern void _PyUnicode_Fini(PyInterpreterState *);
 extern void _PyUnicode_FiniTypes(PyInterpreterState *);
 extern void _PyStaticUnicode_Dealloc(PyObject *);
 
+extern PyTypeObject _PyUnicodeASCIIIter_Type;
 
 /* other API */
 

Lib/test/test_unicode.py

@@ -9,6 +9,7 @@
 import codecs
 import itertools
 import operator
+import pickle
 import struct
 import sys
 import textwrap
@@ -185,6 +186,36 @@ def test_iterators(self):
         self.assertEqual(next(it), "\u3333")
         self.assertRaises(StopIteration, next, it)
 
+    def test_iterators_invocation(self):
+        cases = [type(iter('abc')), type(iter('🚀'))]
+        for cls in cases:
+            with self.subTest(cls=cls):
+                self.assertRaises(TypeError, cls)
+
+    def test_iteration(self):
+        cases = ['abc', '🚀🚀🚀', "\u1111\u2222\u3333"]
+        for case in cases:
+            with self.subTest(string=case):
+                self.assertEqual(case, "".join(iter(case)))
+
+    def test_exhausted_iterator(self):
+        cases = ['abc', '🚀🚀🚀', "\u1111\u2222\u3333"]
+        for case in cases:
+            with self.subTest(case=case):
+                iterator = iter(case)
+                tuple(iterator)
+                self.assertRaises(StopIteration, next, iterator)
+
+    def test_pickle_iterator(self):
+        cases = ['abc', '🚀🚀🚀', "\u1111\u2222\u3333"]
+        for case in cases:
+            with self.subTest(case=case):
+                for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+                    it = iter(case)
+                    with self.subTest(proto=proto):
+                        pickled = "".join(pickle.loads(pickle.dumps(it, proto)))
+                        self.assertEqual(case, pickled)
+
     def test_count(self):
         string_tests.CommonTest.test_count(self)
         # check mixed argument types

Misc/NEWS.d/next/Core and Builtins/2022-04-15-16-57-23.gh-issue-91576.adoDj_.rst

@@ -0,0 +1 @@
+Speed up iteration of ascii strings by 50%. Patch by Kumar Aditya.

Objects/object.c

@@ -1936,6 +1936,7 @@ static PyTypeObject* static_types[] = {
     &_PyNamespace_Type,
     &_PyNone_Type,
     &_PyNotImplemented_Type,
+    &_PyUnicodeASCIIIter_Type,
     &_PyUnion_Type,
     &_PyWeakref_CallableProxyType,
     &_PyWeakref_ProxyType,

Objects/unicodeobject.c

@@ -15697,7 +15697,7 @@ unicodeiter_traverse(unicodeiterobject *it, visitproc visit, void *arg)
 static PyObject *
 unicodeiter_next(unicodeiterobject *it)
 {
-    PyObject *seq, *item;
+    PyObject *seq;
 
     assert(it != NULL);
     seq = it->it_seq;
@@ -15709,17 +15709,38 @@ unicodeiter_next(unicodeiterobject *it)
         int kind = PyUnicode_KIND(seq);
         const void *data = PyUnicode_DATA(seq);
         Py_UCS4 chr = PyUnicode_READ(kind, data, it->it_index);
-        item = PyUnicode_FromOrdinal(chr);
-        if (item != NULL)
-            ++it->it_index;
-        return item;
+        it->it_index++;
+        return unicode_char(chr);
     }
 
     it->it_seq = NULL;
     Py_DECREF(seq);
     return NULL;
 }
 
+static PyObject *
+unicode_ascii_iter_next(unicodeiterobject *it)
+{
+    assert(it != NULL);
+    PyObject *seq = it->it_seq;
+    if (seq == NULL) {
+        return NULL;
+    }
+    assert(_PyUnicode_CHECK(seq));
+    assert(PyUnicode_IS_COMPACT_ASCII(seq));
+    if (it->it_index < PyUnicode_GET_LENGTH(seq)) {
+        const void *data = ((void*)(_PyASCIIObject_CAST(seq) + 1));
+        Py_UCS1 chr = (Py_UCS1)PyUnicode_READ(PyUnicode_1BYTE_KIND,
+                                              data, it->it_index);
+        it->it_index++;
+        PyObject *item = (PyObject*)&_Py_SINGLETON(strings).ascii[chr];
+        return Py_NewRef(item);
+    }
+    it->it_seq = NULL;
+    Py_DECREF(seq);
+    return NULL;
+}
+
 static PyObject *
 unicodeiter_len(unicodeiterobject *it, PyObject *Py_UNUSED(ignored))
 {
@@ -15808,6 +15829,19 @@ PyTypeObject PyUnicodeIter_Type = {
     0,
 };
 
+PyTypeObject _PyUnicodeASCIIIter_Type = {
+    PyVarObject_HEAD_INIT(&PyType_Type, 0)
+    .tp_name = "str_ascii_iterator",
+    .tp_basicsize = sizeof(unicodeiterobject),
+    .tp_dealloc = (destructor)unicodeiter_dealloc,
+    .tp_getattro = PyObject_GenericGetAttr,
+    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
+    .tp_traverse = (traverseproc)unicodeiter_traverse,
+    .tp_iter = PyObject_SelfIter,
+    .tp_iternext = (iternextfunc)unicode_ascii_iter_next,
+    .tp_methods = unicodeiter_methods,
+};
+
 static PyObject *
 unicode_iter(PyObject *seq)
 {
@@ -15819,7 +15853,12 @@ unicode_iter(PyObject *seq)
     }
     if (PyUnicode_READY(seq) == -1)
         return NULL;
-    it = PyObject_GC_New(unicodeiterobject, &PyUnicodeIter_Type);
+    if (PyUnicode_IS_COMPACT_ASCII(seq)) {
+        it = PyObject_GC_New(unicodeiterobject, &_PyUnicodeASCIIIter_Type);
+    }
+    else {
+        it = PyObject_GC_New(unicodeiterobject, &PyUnicodeIter_Type);
+    }
     if (it == NULL)
         return NULL;
     it->it_index = 0;