@@ -143,6 +143,15 @@ repos:
         entry: Space found in path, move to Misc/NEWS.d/next/Core_and_Builtins/
         files: Misc/NEWS.d/next/Core and Builtins/20.*.rst
 
+  - repo: local
+    hooks:
+      - id: check-capi-macros
+        name: Check C API macros start with Py
+        language: python
+        entry: python Tools/build/check_capi_macros.py
+        pass_filenames: false
+        files: ^(Include/(cpython/)?[^/]+\.h|pyconfig\.h\.in|Tools/build/check_capi_macros)
+
   - repo: meta
     hooks:
       - id: check-hooks-apply

diff --git a/Tools/build/check_capi_macros.py b/Tools/build/check_capi_macros.py
@@ -0,0 +1,170 @@
+"""
+Check that all macros defined by the Python C API have a name starting with
+"Py". Ignore names listed by check_capi_macros_ignored.txt: macros with an
+invalid name, added before this script was created.
+
+Python C API:
+
+* Include/*.h
+* Include/cpython/*.h
+* pyconfig.h.in
+"""
+
+import difflib
+import glob
+import os.path
+import re
+import sys
+
+EXCLUDE_HEADERS = {
+    # Header files not included by Python.h and ignored by this script
+    'dynamic_annotations.h',
+    'errcode.h',
+    'opcode.h',
+    'opcode_ids.h',
+    'osdefs.h',
+    'pyexpat.h',
+    'structmember.h',
+
+    # Header files not included by Python.h but parsed by this script:
+    # - datetime.h
+    # - frameobject.h
+    # - marshal.h
+    # - py_curses.h
+    # - pydtrace.h
+}
+
+TOOLS_BUILD_DIR = os.path.abspath(os.path.dirname(__file__))
+SRC_DIR = os.path.dirname(os.path.dirname(TOOLS_BUILD_DIR))
+IGNORED_FILENAME = os.path.join(TOOLS_BUILD_DIR, 'check_capi_macros_ignored.txt')
+
+DEFINE_REGEX = re.compile(r'\s*#\s*(?P<directive>define|undef)\s+(?P<macro>.*)')
+PYTHON_PREFIX = re.compile(r'(Py|PY|_Py|_PY)')
+NAME_REGEX = re.compile(r'([A-Za-z_][A-Za-z0-9_]*)\b')
+
+CAUSES_BY_DIRECTIVE = {
+    "define": "defined",
+    "undef": "undefined",
+}
+
+
+def parse_file(filename, names):
+    with open(filename, encoding='utf8') as fp:
+        for lineno, line in enumerate(fp, start=1):
+            # Check for '#define MACRO'
+            match = DEFINE_REGEX.match(line)
+            if not match:
+                continue
+            macro = match['macro']
+            directive = match['directive']
+            cause = CAUSES_BY_DIRECTIVE.get(directive, directive)
+
+            if PYTHON_PREFIX.match(macro):
+                continue
+
+            match = NAME_REGEX.match(macro)
+            if not match:
+                print(f"ERROR: {filename}: Unable to parse {line!r}")
+                sys.exit(1)
+            name = match[1]
+            names.append((name, filename, lineno, cause))
+
+
+def get_ignored_names():
+    ignored = []
+    with open(IGNORED_FILENAME, encoding='utf8') as fp:
+        for line in fp:
+            name = line.strip()
+            if name.startswith('#'):
+                # Ignore comment
+                continue
+            if name:
+                ignored.append(name)
+    return ignored
+
+
+def main():
+    failure = False
+
+    # Parse header files
+    include_dir = os.path.join(SRC_DIR, 'Include')
+    files = glob.glob(os.path.join(include_dir, '*.h'))
-    files = glob.glob(os.path.join(include_dir, '*.h'))
+    files = glob.glob(os.path.join(include_dir, '*.h'))
+    files.remove(os.path.join(include_dir, 'opcode_ids.h'))
-    files = glob.glob(os.path.join(include_dir, '*.h'))
+    files = glob.glob(os.path.join(include_dir, '*.h'))
+    files.remove(os.path.join(include_dir, 'opcode_ids.h'))
+    files = [filename for filename in files
+             if os.path.basename(filename) not in EXCLUDE_HEADERS]
+    files.extend(glob.glob(os.path.join(include_dir, 'cpython', '*.h')))
+    files.append(os.path.join(SRC_DIR, 'pyconfig.h.in'))
+    names = []  # list of (name: str, filename: str, lineno: int, cause: str)
+    for filename in files:
+        parse_file(filename, names)
+
+    # Parse ignore list
+    ignored = get_ignored_names()
+
+    # Check if the sorted list has duplicated entries
+    if len(set(ignored)) != len(ignored):
+        print(f"ERROR: {IGNORED_FILENAME} list contains duplicated entries:")
+        print()
+        seen = set()
+        for name in ignored:
+            if name not in seen:
+                seen.add(name)
+                continue
+            print(f"- {name}")
+        print()
+        failure = True
+
+    # Check if the sorted list is sorted
+    ignored_sorted = sorted(ignored)
+    if ignored_sorted != ignored:
+        print(f"ERROR: {IGNORED_FILENAME} list is not sorted")
+        print()
+        diff = difflib.unified_diff(ignored, ignored_sorted,
+                                    fromfile=IGNORED_FILENAME,
+                                    tofile=IGNORED_FILENAME,
+                                    lineterm='')
+        for line in diff:
+            print(line)
+        print()
+        failure = True
+
+    # Check for outdated ignore list
+    names_set = {name for name, filename, lineno, cause in names}
+    ignored = set(ignored)
+    outdated = ignored - names_set
+    if outdated:
+        print(f"ERROR: {IGNORED_FILENAME} is outdated, "
+              "the following macros can be removed:")
+        print()
+        for name in sorted(outdated):
+            print(f"- {name}")
+        print()
+        print(f"Total: {len(outdated)} macros")
+        print()
+        failure = True
+
+    # Check for new macros
+    new_macros = names_set - ignored
+    if new_macros:
+        print('ERROR: the Python C API defines the following new macros:')
+        print()
+        count = 0
+        for name, filename, lineno, cause in sorted(names):
+            if name in ignored:
+                continue
+            print(f"- {name} {cause} at {filename}:{lineno}")
+            count += 1
+        print()
+        print(f"Total: {count} macros")
+        failure = True
+
+    if not failure:
+        print("OK: the ignore list is up to date and sorted")
+        print("OK: the Python C API only defines macros with names "
+              f"starting with Py (ignoring {len(ignored)} macros)")
+        sys.exit(0)
+
+    sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()