issue #3554: ctypes.string_at and ctypes.wstring_at must use the

pythonapi calling convention so that the GIL is held and error return
values are checked.

Lib/ctypes/__init__.py

@@ -485,7 +485,7 @@ _cast = PYFUNCTYPE(py_object, c_void_p, py_object, py_object)(_cast_addr)
 def cast(obj, typ):
     return _cast(obj, obj, typ)
 
-_string_at = CFUNCTYPE(py_object, c_void_p, c_int)(_string_at_addr)
+_string_at = PYFUNCTYPE(py_object, c_void_p, c_int)(_string_at_addr)
 def string_at(ptr, size=-1):
     """string_at(addr[, size]) -> string
 
@@ -497,7 +497,7 @@ try:
 except ImportError:
     pass
 else:
-    _wstring_at = CFUNCTYPE(py_object, c_void_p, c_int)(_wstring_at_addr)
+    _wstring_at = PYFUNCTYPE(py_object, c_void_p, c_int)(_wstring_at_addr)
     def wstring_at(ptr, size=-1):
         """wstring_at(addr[, size]) -> string
 

Misc/NEWS

@@ -77,6 +77,10 @@ Core and builtins
 Library
 -------
 
+- Issue #3554: ctypes.string_at and ctypes.wstring_at did call Python
+  api functions without holding the GIL, which could lead to a fatal
+  error when they failed.
+
 - Issue #2234: distutils failed for some versions of the cygwin compiler. The
   version reported by these tools does not necessarily follow the python
   version numbering scheme, so the module is less strict when parsing it.