GH-2854: Reimplement absolute module imports to speed them up, especially...

GH-2854: Reimplement absolute module imports to speed them up, especially under Py3.7. Cython used to be 3x slower than CPython here.
Also enable absolute imports automatically in top-level (non-package) modules.

Cython/Compiler/ExprNodes.py

@@ -2527,44 +2527,61 @@ class ImportNode(ExprNode):
     #                           relative to the current module.
     #                     None: decide the level according to language level and
     #                           directives
+    #  get_top_level_module   int          true: return top-level module, false: return imported module
+    #  module_names           TupleNode    the separate names of the module and submodules, or None
 
     type = py_object_type
+    module_names = None
+    get_top_level_module = False
+    is_temp = True
 
-    subexprs = ['module_name', 'name_list']
+    subexprs = ['module_name', 'name_list', 'module_names']
 
     def analyse_types(self, env):
         if self.level is None:
-            if (env.directives['py2_import'] or
-                Future.absolute_import not in env.global_scope().context.future_directives):
+            # For modules in packages, and without 'absolute_import' enabled, try relative (Py2) import first.
+            if env.global_scope().parent_module and (
+                    env.directives['py2_import'] or
+                    Future.absolute_import not in env.global_scope().context.future_directives):
                 self.level = -1
             else:
                 self.level = 0
         module_name = self.module_name.analyse_types(env)
         self.module_name = module_name.coerce_to_pyobject(env)
+        assert self.module_name.is_string_literal
         if self.name_list:
             name_list = self.name_list.analyse_types(env)
             self.name_list = name_list.coerce_to_pyobject(env)
-        self.is_temp = 1
+        elif '.' in self.module_name.value:
+            self.module_names = TupleNode(self.module_name.pos, args=[
+                IdentifierStringNode(self.module_name.pos, value=part, constant_result=part)
+                for part in map(StringEncoding.EncodedString, self.module_name.value.split('.'))
+            ]).analyse_types(env)
         return self
 
     gil_message = "Python import"
 
     def generate_result_code(self, code):
-        if self.name_list:
-            name_list_code = self.name_list.py_result()
+        assert self.module_name.is_string_literal
+        module_name = self.module_name.value
+
+        if self.level == 0 and not self.name_list and not self.get_top_level_module:
+            if self.module_names:
+                assert self.module_names.is_literal  # make sure we create the tuple only once
+            code.globalstate.use_utility_code(UtilityCode.load_cached("ImportDottedModule", "ImportExport.c"))
+            import_code = "__Pyx_ImportDottedModule(%s, %s)" % (
+                self.module_name.py_result(),
+                self.module_names.py_result() if self.module_names else 'NULL',
+            )
         else:
-            name_list_code = "0"
-
-        code.globalstate.use_utility_code(UtilityCode.load_cached("Import", "ImportExport.c"))
-        import_code = "__Pyx_Import(%s, %s, %d)" % (
-            self.module_name.py_result(),
-            name_list_code,
-            self.level)
+            code.globalstate.use_utility_code(UtilityCode.load_cached("Import", "ImportExport.c"))
+            import_code = "__Pyx_Import(%s, %s, %d)" % (
+                self.module_name.py_result(),
+                self.name_list.py_result() if self.name_list else '0',
+                self.level)
 
-        if (self.level <= 0 and
-                self.module_name.is_string_literal and
-                self.module_name.value in utility_code_for_imports):
-            helper_func, code_name, code_file = utility_code_for_imports[self.module_name.value]
+        if self.level <= 0 and module_name in utility_code_for_imports:
+            helper_func, code_name, code_file = utility_code_for_imports[module_name]
             code.globalstate.use_utility_code(UtilityCode.load_cached(code_name, code_file))
             import_code = '%s(%s)' % (helper_func, import_code)
 

Cython/Compiler/Parsing.py

@@ -1675,11 +1675,6 @@ def p_import_statement(s):
                 as_name=as_name,
                 is_absolute=is_absolute)
         else:
-            if as_name and "." in dotted_name:
-                name_list = ExprNodes.ListNode(pos, args=[
-                    ExprNodes.IdentifierStringNode(pos, value=s.context.intern_ustring("*"))])
-            else:
-                name_list = None
             stat = Nodes.SingleAssignmentNode(
                 pos,
                 lhs=ExprNodes.NameNode(pos, name=as_name or target_name),
@@ -1687,7 +1682,8 @@ def p_import_statement(s):
                     pos,
                     module_name=ExprNodes.IdentifierStringNode(pos, value=dotted_name),
                     level=0 if is_absolute else None,
-                    name_list=name_list))
+                    get_top_level_module='.' in dotted_name and as_name is None,
+                    name_list=None))
         stats.append(stat)
     return Nodes.StatListNode(pos, stats=stats)
 

Cython/Utility/ImportExport.c

@@ -9,6 +9,135 @@
 #endif
 
 
+/////////////// ImportDottedModule.proto ///////////////
+
+static PyObject *__Pyx_ImportDottedModule(PyObject *name, PyObject *parts_tuple); /*proto*/
+
+/////////////// ImportDottedModule ///////////////
+//@requires: Import
+
+#if PY_MAJOR_VERSION >= 3
+static PyObject *__Pyx__ImportDottedModule_Error(PyObject *name, PyObject *parts_tuple, Py_ssize_t count) {
+    PyObject *partial_name = NULL, *slice = NULL, *sep = NULL;
+    if (unlikely(PyErr_Occurred())) {
+        PyErr_Clear();
+    }
+    if (likely(PyTuple_GET_SIZE(parts_tuple) == count)) {
+        partial_name = name;
+    } else {
+        PyObject *sep;
+        PyObject *slice = PySequence_GetSlice(parts_tuple, 0, count);
+        if (unlikely(!slice))
+            goto bad;
+        sep = PyUnicode_FromStringAndSize(".", 1);
+        if (unlikely(!sep))
+            goto bad;
+        partial_name = PyUnicode_Join(sep, slice);
+    }
+
+    PyErr_Format(
+#if PY_MAJOR_VERSION < 3
+        PyExc_ImportError,
+        "No module named '%s'", PyString_AS_STRING(partial_name));
+#else
+#if PY_VERSION_HEX >= 0x030600B1
+        PyExc_ModuleNotFoundError,
+#else
+        PyExc_ImportError,
+#endif
+        "No module named '%U'", partial_name);
+#endif
+
+bad:
+    Py_XDECREF(sep);
+    Py_XDECREF(slice);
+    Py_XDECREF(partial_name);
+    return NULL;
+}
+#endif
+
+static PyObject *__Pyx__ImportDottedModule(PyObject *name, CYTHON_UNUSED PyObject *parts_tuple) {
+#if PY_MAJOR_VERSION < 3
+    PyObject *module, *from_list = NULL, *star = PYIDENT("*");
+    from_list = PyList_New(1);
+    if (unlikely(!from_list))
+        return NULL;
+    Py_INCREF(star);
+    PyList_SET_ITEM(from_list, 0, star);
+    module = __Pyx_Import(name, from_list, 0);
+    Py_DECREF(from_list);
+    return module;
+#else
+    Py_ssize_t i, nparts;
+    PyObject *module = __Pyx_Import(name, NULL, 0);
+    if (!parts_tuple || unlikely(!module))
+        return module;
+
+    nparts = PyTuple_GET_SIZE(parts_tuple);
+    for (i=1; i < nparts && module; i++) {
+        PyObject *part, *submodule;
+#if CYTHON_ASSUME_SAFE_MACROS && !CYTHON_AVOID_BORROWED_REFS
+        part = PyTuple_GET_ITEM(parts_tuple, i);
+#else
+        part = PySequence_ITEM(parts_tuple, i);
+#endif
+        submodule = __Pyx_PyObject_GetAttrStrNoError(module, part);
+#if !(CYTHON_ASSUME_SAFE_MACROS && !CYTHON_AVOID_BORROWED_REFS)
+        Py_DECREF(part);
+#endif
+        Py_DECREF(module);
+        module = submodule;
+    }
+    if (likely(module))
+        return module;
+    return __Pyx__ImportDottedModule_Error(name, parts_tuple, i);
+#endif
+}
+
+static PyObject *__Pyx_ImportDottedModule(PyObject *name, PyObject *parts_tuple) {
+#if CYTHON_COMPILING_IN_CPYTHON && PY_VERSION_HEX >= 0x030400B1
+    PyObject *module;
+    #if PY_VERSION_HEX < 0x030700A1
+    PyObject *modules = PyImport_GetModuleDict();
+    if (unlikely(!modules))
+        return NULL;
+    module = __Pyx_PyDict_GetItemStr(modules, name);
+    Py_XINCREF(module);
+    #else
+    module = PyImport_GetModule(name);
+    #endif
+    if (likely(module)) {
+        // TODO: CPython guards against thread-concurrent imports in importlib,
+        // but importing and calling into importlib just for that rare case would
+        // be quite costly, so we skip it for now.
+        return module;
+
+// -- Code copied from Py3.8-pre:
+//        PyObject *spec = __Pyx_PyObject_GetAttrStrNoError(module, PYIDENT("__spec__"));
+//        if (likely(spec)) {
+//            PyObject *unsafe = __Pyx_PyObject_GetAttrStrNoError(spec, PYIDENT("_initializing"));
+//            if (likely(!unsafe || !__Pyx_PyObject_IsTrue(unsafe))) {
+//                Py_DECREF(spec);
+//                spec = NULL;
+//            }
+//            Py_XDECREF(unsafe);
+//        }
+//        if (likely(!spec)) {
+//            PyErr_Clear();
+//            return module;
+//        }
+//        Py_DECREF(spec);
+//        // Need to let PyImport_ImportModuleLevelObject() handle the locking.
+//        Py_DECREF(module);
+    } else if (PyErr_Occurred()) {
+        PyErr_Clear();
+    }
+#endif
+
+    return __Pyx__ImportDottedModule(name, parts_tuple);
+}
+
+
 /////////////// Import.proto ///////////////
 
 static PyObject *__Pyx_Import(PyObject *name, PyObject *from_list, int level); /*proto*/
@@ -18,30 +147,23 @@ static PyObject *__Pyx_Import(PyObject *name, PyObject *from_list, int level); /
 //@substitute: naming
 
 static PyObject *__Pyx_Import(PyObject *name, PyObject *from_list, int level) {
-    PyObject *empty_list = 0;
     PyObject *module = 0;
-    PyObject *global_dict = 0;
     PyObject *empty_dict = 0;
-    PyObject *list;
+    PyObject *empty_list = 0;
     #if PY_MAJOR_VERSION < 3
     PyObject *py_import;
     py_import = __Pyx_PyObject_GetAttrStr($builtins_cname, PYIDENT("__import__"));
-    if (!py_import)
+    if (unlikely(!py_import))
         goto bad;
-    #endif
-    if (from_list)
-        list = from_list;
-    else {
+    if (!from_list) {
         empty_list = PyList_New(0);
-        if (!empty_list)
+        if (unlikely(!empty_list))
             goto bad;
-        list = empty_list;
+        from_list = empty_list;
     }
-    global_dict = PyModule_GetDict($module_cname);
-    if (!global_dict)
-        goto bad;
+    #endif
     empty_dict = PyDict_New();
-    if (!empty_dict)
+    if (unlikely(!empty_dict))
         goto bad;
     {
         #if PY_MAJOR_VERSION >= 3
@@ -49,9 +171,9 @@ static PyObject *__Pyx_Import(PyObject *name, PyObject *from_list, int level) {
             if (strchr(__Pyx_MODULE_NAME, '.')) {
                 /* try package relative import first */
                 module = PyImport_ImportModuleLevelObject(
-                    name, global_dict, empty_dict, list, 1);
-                if (!module) {
-                    if (!PyErr_ExceptionMatches(PyExc_ImportError))
+                    name, $moddict_cname, empty_dict, from_list, 1);
+                if (unlikely(!module)) {
+                    if (unlikely(!PyErr_ExceptionMatches(PyExc_ImportError)))
                         goto bad;
                     PyErr_Clear();
                 }
@@ -62,23 +184,23 @@ static PyObject *__Pyx_Import(PyObject *name, PyObject *from_list, int level) {
         if (!module) {
             #if PY_MAJOR_VERSION < 3
             PyObject *py_level = PyInt_FromLong(level);
-            if (!py_level)
+            if (unlikely(!py_level))
                 goto bad;
             module = PyObject_CallFunctionObjArgs(py_import,
-                name, global_dict, empty_dict, list, py_level, (PyObject *)NULL);
+                name, $moddict_cname, empty_dict, from_list, py_level, (PyObject *)NULL);
             Py_DECREF(py_level);
             #else
             module = PyImport_ImportModuleLevelObject(
-                name, global_dict, empty_dict, list, level);
+                name, $moddict_cname, empty_dict, from_list, level);
             #endif
         }
     }
 bad:
+    Py_XDECREF(empty_dict);
+    Py_XDECREF(empty_list);
     #if PY_MAJOR_VERSION < 3
     Py_XDECREF(py_import);
     #endif
-    Py_XDECREF(empty_list);
-    Py_XDECREF(empty_dict);
     return module;
 }
 

tests/run/importas.pyx

+# mode: run
+# tag: all_language_levels
+
 __doc__ = u"""
+>>> try: sys
+... except NameError: pass
+... else: print("sys was defined!")
+>>> try: distutils
+... except NameError: pass
+... else: print("distutils was defined!")
+
 >>> import sys as sous
 >>> import distutils.core as corey
 >>> from copy import deepcopy as copey

tests/run/reimport_from_package.srctree

@@ -17,8 +17,8 @@ setup(
 
 import sys
 import a
-assert a in sys.modules.values(), list(sys.modules)
-assert sys.modules['a'] is a, list(sys.modules)
+assert a in sys.modules.values(), sorted(sys.modules)
+assert sys.modules['a'] is a, sorted(sys.modules)
 
 from atest.package import module
 
@@ -33,8 +33,8 @@ assert 'atest.package.module' in sys.modules
 
 import a
 import atest.package.module as module
-assert module in sys.modules.values(), list(sys.modules)
-assert sys.modules['atest.package.module'] is module, list(sys.modules)
+assert module in sys.modules.values(), sorted(sys.modules)
+assert sys.modules['atest.package.module'] is module, sorted(sys.modules)
 
 if sys.version_info >= (3, 5):
     from . import pymodule

tests/run/relativeimport_T542.srctree

@@ -26,7 +26,8 @@ try:
 except ImportError:
     pass
 else:
-    assert False, "absolute import succeeded"
+    import sys
+    assert False, "absolute import succeeded: %s" % sorted(sys.modules)
 
 import relimport.a
 import relimport.bmod