Avoid ctypes import on unsupported platforms

Author: jakelishman

Lib/test/support/__init__.py

@@ -5,7 +5,6 @@
 
 import annotationlib
 import contextlib
-import ctypes
 import functools
 import inspect
 import logging
@@ -3187,20 +3186,25 @@ def linked_to_musl():
     return _linked_to_musl
 
 
-class _py_buffer(ctypes.Structure):
-    _fields_ = [
-        ("buf", ctypes.c_void_p),
-        ("obj", ctypes.py_object),
-        ("len", ctypes.c_ssize_t),
-        ("itemsize", ctypes.c_ssize_t),
-        ("readonly", ctypes.c_int),
-        ("ndim", ctypes.c_int),
-        ("format", ctypes.c_char_p),
-        ("shape", ctypes.POINTER(ctypes.c_ssize_t)),
-        ("strides", ctypes.POINTER(ctypes.c_ssize_t)),
-        ("suboffsets", ctypes.POINTER(ctypes.c_ssize_t)),
-        ("internal", ctypes.c_void_p),
-    ]
+try:
+    import ctypes
+
+    class _py_buffer(ctypes.Structure):
+        _fields_ = [
+            ("buf", ctypes.c_void_p),
+            ("obj", ctypes.py_object),
+            ("len", ctypes.c_ssize_t),
+            ("itemsize", ctypes.c_ssize_t),
+            ("readonly", ctypes.c_int),
+            ("ndim", ctypes.c_int),
+            ("format", ctypes.c_char_p),
+            ("shape", ctypes.POINTER(ctypes.c_ssize_t)),
+            ("strides", ctypes.POINTER(ctypes.c_ssize_t)),
+            ("suboffsets", ctypes.POINTER(ctypes.c_ssize_t)),
+            ("internal", ctypes.c_void_p),
+        ]
+except ImportError:
+    _py_buffer = None
 
 
 @contextlib.contextmanager
@@ -3210,7 +3214,12 @@ def ctypes_py_buffer(ob, flags=inspect.BufferFlags.SIMPLE):
 
     `ob` must implement the buffer protocol, and the retrieved buffer is
     released on exit of the context manager.
+
+    Skips any test using it if `ctypes` is unavailable.
     """
+    from .import_helper import import_module
+
+    ctypes = import_module("ctypes")
     buf = _py_buffer()
     ctypes.pythonapi.PyObject_GetBuffer(ctypes.py_object(ob),
                                         ctypes.byref(buf),

Lib/test/test_array.py

@@ -9,7 +9,6 @@
 from test.support import os_helper
 from test.support import _2G
 from test.support import ctypes_py_buffer
-import ctypes
 import weakref
 import pickle
 import operator
@@ -71,6 +70,7 @@ def test_empty(self):
 
     def test_empty_alignment(self):
         # gh-140557: pointer alignment of empty allocation
+        ctypes = import_helper.import_module("ctypes")
         self.enterContext(warnings.catch_warnings())
         warnings.filterwarnings(
             "ignore",

Lib/test/test_builtin.py

@@ -4,7 +4,6 @@
 import builtins
 import collections
 import contextlib
-import ctypes
 import decimal
 import fractions
 import gc
@@ -2408,6 +2407,7 @@ def iterator():
 
     def test_bytearray_empty_alignment(self):
         # gh-140557: alignment of pointer in empty allocation
+        ctypes = import_module("ctypes")
         max_align = ctypes.alignment(ctypes.c_longdouble)
         array = bytearray()
         with ctypes_py_buffer(array) as buf: