python · vstinner · Feb 17, 2026 · corona10 · Feb 19, 2026 · vstinner
diff --git a/Doc/library/errno.rst b/Doc/library/errno.rst
@@ -18,6 +18,9 @@ all-inclusive.
   underlying system.  For instance, ``errno.errorcode[errno.EPERM]`` maps to
   ``'EPERM'``.

+   .. versionchanged:: next
+      The dictionary type is now a :class:`frozendict`.
+
 To translate a numeric error code to an error message, use :func:`os.strerror`.

 Of the following list, symbols that are not used on the current platform are not

diff --git a/Lib/test/test_errno.py b/Lib/test/test_errno.py
@@ -19,6 +19,10 @@ def test_using_errorcode(self):
        for value in errno.errorcode.values():
            self.assertHasAttr(errno, value)

+    def test_readonly_errorcode(self):
+        with self.assertRaises(TypeError):
+            errno.errorcode[1] = 'hack'
+

 class ErrorcodeTests(unittest.TestCase):


diff --git a/Misc/NEWS.d/next/Library/2026-02-17-12-26-53.gh-issue-141510.tQcHWz.rst b/Misc/NEWS.d/next/Library/2026-02-17-12-26-53.gh-issue-141510.tQcHWz.rst
@@ -0,0 +1,2 @@
+:data:`errno.errorcode` is now read-only: use :class:`frozendict` type
+instead of :class:`dict`. Patch by Victor Stinner.
diff --git a/Modules/errnomodule.c b/Modules/errnomodule.c
@@ -1,11 +1,5 @@
 /* Errno module */

-// Need limited C API version 3.13 for Py_mod_gil
-#include "pyconfig.h"   // Py_GIL_DISABLED
-#ifndef Py_GIL_DISABLED
-#  define Py_LIMITED_API 0x030d0000
-#endif
-
 #include "Python.h"
 #include <errno.h>                // EPIPE

@@ -96,10 +90,6 @@ errno_exec(PyObject *module)
    if (error_dict == NULL) {
        return -1;
    }
-    if (PyDict_SetItemString(module_dict, "errorcode", error_dict) < 0) {
-        Py_DECREF(error_dict);
-        return -1;
-    }

 /* Macro so I don't have to edit each and every line below... */
 #define add_errcode(name, code, comment)                               \
@@ -947,7 +937,17 @@ errno_exec(PyObject *module)
    add_errcode("ENOTCAPABLE", ENOTCAPABLE, "Capabilities insufficient");
 #endif

+    PyObject *frozendict = PyFrozenDict_New(error_dict);
    Py_DECREF(error_dict);
+    if (frozendict == NULL) {
+        return -1;
+    }
+    if (PyDict_SetItemString(module_dict, "errorcode", frozendict) < 0) {
+        Py_DECREF(frozendict);
+        return -1;
+    }
+    Py_DECREF(frozendict);
+
    return 0;
 }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		:data:`errno.errorcode` is now read-only: use :class:`frozendict` type
		instead of :class:`dict`. Patch by Victor Stinner.
-Original file line number
+Diff line change
@@ -1,11 +1,5 @@
     /* Errno module */
-    // Need limited C API version 3.13 for Py_mod_gil
-    #include "pyconfig.h"   // Py_GIL_DISABLED
-    #ifndef Py_GIL_DISABLED
-    #  define Py_LIMITED_API 0x030d0000
-    #endif
     #include "Python.h"
     #include <errno.h>                // EPIPE
@@ -96,10 +90,6 @@ errno_exec(PyObject *module)
         if (error_dict == NULL) {
             return -1;
         }
-        if (PyDict_SetItemString(module_dict, "errorcode", error_dict) < 0) {
-            Py_DECREF(error_dict);
-            return -1;
-        }
     /* Macro so I don't have to edit each and every line below... */
     #define add_errcode(name, code, comment)                               \
@@ -947,7 +937,17 @@ errno_exec(PyObject *module)
         add_errcode("ENOTCAPABLE", ENOTCAPABLE, "Capabilities insufficient");
     #endif
+        PyObject *frozendict = PyFrozenDict_New(error_dict);
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            corona10
  

      

      

      


        Feb 19, 2026



      
    

  

  
    
      
          
    
  


        
            
  
      
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      I think that we have to add new C API for frozendict with builder pattern.

This is inefficient for many people.
    
  
  



    

        
      
  
  
    
  
  
  
    
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            vstinner
  

      

      

      


        Feb 19, 2026



      
    

  

  
    
      
          
    
  


        
            
  
      
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      Well, frozendict is not widely used in C code yet. IMO it's too early to design an optimized API to build a new frozendict object. PyFrozenDict_New() should be good for now.
    
  
  



    

        
      
  
  
    
  
  
  
    
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         Py_DECREF(error_dict);
+        if (frozendict == NULL) {
+            return -1;
+        }
+        if (PyDict_SetItemString(module_dict, "errorcode", frozendict) < 0) {
+            Py_DECREF(frozendict);
+            return -1;
+        }
+        Py_DECREF(frozendict);
         return 0;
     }
-          Expand Down