1 files changed, 64 insertions, 0 deletions
diff --git a/modules/patches.py b/modules/patches.py
new file mode 100644
index 00000000..348235e7
--- /dev/null
+++ b/modules/patches.py
@@ -0,0 +1,64 @@
+from collections import defaultdict
+
+
+def patch(key, obj, field, replacement):
+    """Replaces a function in a module or a class.
+
+    Also stores the original function in this module, possible to be retrieved via original(key, obj, field).
+    If the function is already replaced by this caller (key), an exception is raised -- use undo() before that.
+
+    Arguments:
+        key: identifying information for who is doing the replacement. You can use __name__.
+        obj: the module or the class
+        field: name of the function as a string
+        replacement: the new function
+
+    Returns:
+        the original function
+    """
+
+    patch_key = (obj, field)
+    if patch_key in originals[key]:
+        raise RuntimeError(f"patch for {field} is already applied")
+
+    original_func = getattr(obj, field)
+    originals[key][patch_key] = original_func
+
+    setattr(obj, field, replacement)
+
+    return original_func
+
+
+def undo(key, obj, field):
+    """Undoes the peplacement by the patch().
+
+    If the function is not replaced, raises an exception.
+
+    Arguments:
+        key: identifying information for who is doing the replacement. You can use __name__.
+        obj: the module or the class
+        field: name of the function as a string
+
+    Returns:
+        Always None
+    """
+
+    patch_key = (obj, field)
+
+    if patch_key not in originals[key]:
+        raise RuntimeError(f"there is no patch for {field} to undo")
+
+    original_func = originals[key].pop(patch_key)
+    setattr(obj, field, original_func)
+
+    return None
+
+
+def original(key, obj, field):
+    """Returns the original function for the patch created by the patch() function"""
+    patch_key = (obj, field)
+
+    return originals[key].get(patch_key, None)
+
+
+originals = defaultdict(dict)