bpo-41842: Add a unregister function in _codecs module

Doc/c-api/codec.rst

@@ -10,6 +10,14 @@ Codec registry and support functions
  As side effect, this tries to load the :mod:`encodings` package, if not yet
  done, to make sure that it is always first in the list of search functions.
 
+.. c:function:: int PyCodec_Unregister(PyObject *search_function)
+
+ Unregister a codec search function and clear the registry's cache.
+ If the search function is not registered, do nothing.
+ Return 0 on success. Raise an exception and return -1 on error.
+
+ .. versionadded:: 3.10
+
 .. c:function:: int PyCodec_KnownEncoding(const char *encoding)
 
  Return ``1`` or ``0`` depending on whether there is a registered codec for

Doc/library/codecs.rst

@@ -163,11 +163,14 @@ function:
  :class:`CodecInfo` object. In case a search function cannot find
  a given encoding, it should return ``None``.
 
- .. note::
 
- Search function registration is not currently reversible,
- which may cause problems in some cases, such as unit testing or
- module reloading.
+.. function:: unregister(search_function)
+
+ Unregister a codec search function and clear the registry's cache.
+ If the search function is not registered, do nothing.
+
+ .. versionadded:: 3.10
+
 
 While the builtin :func:`open` and the associated :mod:`io` module are the
 recommended approach for working with encoded text files, this module

Doc/whatsnew/3.10.rst

@@ -109,6 +109,12 @@ base64
 Add :func:`base64.b32hexencode` and :func:`base64.b32hexdecode` to support the
 Base32 Encoding with Extended Hex Alphabet.
 
+codecs
+------
+
+Add a :func:`codecs.unregister` function to unregister a codec search function.
+(Contributed by Hai Shi in :issue:`41842`.)
+
 curses
 ------
 
@@ -237,6 +243,10 @@ New Features
  :class:`datetime.time` objects.
  (Contributed by Zackery Spytz in :issue:`30155`.)
 
+* Add a :c:func:`PyCodec_Unregister` function to unregister a codec
+ search function.
+ (Contributed by Hai Shi in :issue:`41842`.)
+
 Porting to Python 3.10
 ----------------------
 

Include/codecs.h

@@ -27,6 +27,14 @@ PyAPI_FUNC(int) PyCodec_Register(
  PyObject *search_function
  );
 
+/* Unregister a codec search function and clear the registry's cache.
+ If the search function is not registered, do nothing.
+ Return 0 on success. Raise an exception and return -1 on error. */
+
+PyAPI_FUNC(int) PyCodec_Unregister(
+ PyObject *search_function
+ );
+
 /* Codec registry lookup API.
 
  Looks up the given encoding and returns a CodecInfo object with

Lib/test/test_codecs.py

@@ -1641,6 +1641,18 @@ def test_register(self):
  self.assertRaises(TypeError, codecs.register)
  self.assertRaises(TypeError, codecs.register, 42)
 
+ def test_unregister(self):
+ name = "nonexistent_codec_name"
+ search_function = mock.Mock()
+ codecs.register(search_function)
+ self.assertRaises(TypeError, codecs.lookup, name)
+ search_function.assert_called_with(name)
+ search_function.reset_mock()
+
+ codecs.unregister(search_function)
+ self.assertRaises(LookupError, codecs.lookup, name)
+ search_function.assert_not_called()
+
  def test_lookup(self):
  self.assertRaises(TypeError, codecs.lookup)
  self.assertRaises(LookupError, codecs.lookup, "__spam__")

Misc/ACKS

@@ -1575,6 +1575,7 @@ Akash Shende
 Charlie Shepherd
 Bruce Sherwood
 Gregory Shevchenko
+Hai Shi
 Alexander Shigin
 Pete Shinners
 Michael Shiplett

Misc/NEWS.d/next/C API/2020-09-27-20-43-16.bpo-41842.bCakAj.rst

@@ -0,0 +1,2 @@
+Add :c:func:`PyCodec_Unregister` function to unregister a codec search
+function.

Misc/NEWS.d/next/Library/2020-09-23-22-52-24.bpo-41842.lIuhC9.rst

@@ -0,0 +1 @@
+Add :func:`codecs.unregister` function to unregister a codec search function.

Modules/_codecsmodule.c

@@ -68,6 +68,27 @@ _codecs_register(PyObject *module, PyObject *search_function)
  Py_RETURN_NONE;
 }
 
+/*[clinic input]
+_codecs.unregister
+ search_function: object
+ /
+
+Unregister a codec search function and clear the registry's cache.
+
+If the search function is not registered, do nothing.
+[clinic start generated code]*/
+
+static PyObject *
+_codecs_unregister(PyObject *module, PyObject *search_function)
+/*[clinic end generated code: output=1f0edee9cf246399 input=dd7c004c652d345e]*/
+{
+ if (PyCodec_Unregister(search_function) < 0){
+ return NULL;
+ }
+
+ Py_RETURN_NONE;
+}
+
 /*[clinic input]
 _codecs.lookup
  encoding: str
@@ -992,6 +1013,7 @@ _codecs_lookup_error_impl(PyObject *module, const char *name)
 
 static PyMethodDef _codecs_functions[] ={
  _CODECS_REGISTER_METHODDEF
+ _CODECS_UNREGISTER_METHODDEF
  _CODECS_LOOKUP_METHODDEF
  _CODECS_ENCODE_METHODDEF
  _CODECS_DECODE_METHODDEF

Python/codecs.c

@@ -50,6 +50,31 @@ int PyCodec_Register(PyObject *search_function)
  return -1;
 }
 
+int
+PyCodec_Unregister(PyObject *search_function)
+{
+ PyInterpreterState *interp = PyInterpreterState_Get();
+ PyObject *codec_search_path = interp->codec_search_path;
+ /* Do nothing if codec_search_path is not created yet or was cleared. */
+ if (codec_search_path == NULL){
+ return 0;
+ }
+
+ assert(PyList_CheckExact(codec_search_path));
+ Py_ssize_t n = PyList_GET_SIZE(codec_search_path);
+ for (Py_ssize_t i = 0; i < n; i++){
+ PyObject *item = PyList_GET_ITEM(codec_search_path, i);
+ if (item == search_function){
+ if (interp->codec_search_cache != NULL){
+ assert(PyDict_CheckExact(interp->codec_search_cache));
+ PyDict_Clear(interp->codec_search_cache);
+ }
+ return PyList_SetSlice(codec_search_path, i, i+1, NULL);
+ }
+ }
+ return 0;
+}
+
 extern int _Py_normalize_encoding(const char *, char *, size_t);
 
 /* Convert a string to a normalized Python string(decoded from UTF-8): all characters are