From ecf87ad513fd8af6e4a6093ed918723a7d88d5ca Mon Sep 17 00:00:00 2001
From: yujin <891837834@qq.com>
Date: Tue, 31 Aug 2021 16:14:04 +0800
Subject: [PATCH] Fixed #33099 -- Improved performance of import_string().

This improves performance of import_string() by avoiding multiple
imports for the same path.

Thanks Andrew Godwin and Keryn Knight for the implementation idea.
---
 django/utils/module_loading.py | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/django/utils/module_loading.py b/django/utils/module_loading.py
index 8c798f69bb..1df82b1c32 100644
--- a/django/utils/module_loading.py
+++ b/django/utils/module_loading.py
@@ -1,9 +1,17 @@
 import copy
 import os
+import sys
 from importlib import import_module
 from importlib.util import find_spec as importlib_find
 
 
+def cached_import(module_path, class_name):
+    modules = sys.modules
+    if module_path not in modules:
+        import_module(module_path)
+    return getattr(modules[module_path], class_name)
+
+
 def import_string(dotted_path):
     """
     Import a dotted module path and return the attribute/class designated by the
@@ -14,10 +22,8 @@ def import_string(dotted_path):
     except ValueError as err:
         raise ImportError("%s doesn't look like a module path" % dotted_path) from err
 
-    module = import_module(module_path)
-
     try:
-        return getattr(module, class_name)
+        return cached_import(module_path, class_name)
     except AttributeError as err:
         raise ImportError('Module "%s" does not define a "%s" attribute/class' % (
             module_path, class_name)