bpo-38265: Update os.pread to accept the length type as Py_ssize_t. (GH-16359)

Misc/NEWS.d/next/Library/2019-09-25-05-16-19.bpo-38265.X6-gsT.rst

+Update the *length* parameter of :func:`os.pread` to accept
+:c:type:`Py_ssize_t` instead of :c:type:`int`.

Modules/clinic/posixmodule.c.h

@@ -4799,14 +4799,14 @@ PyDoc_STRVAR(os_pread__doc__,
     {"pread", (PyCFunction)(void(*)(void))os_pread, METH_FASTCALL, os_pread__doc__},
 
 static PyObject *
-os_pread_impl(PyObject *module, int fd, int length, Py_off_t offset);
+os_pread_impl(PyObject *module, int fd, Py_ssize_t length, Py_off_t offset);
 
 static PyObject *
 os_pread(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     int fd;
-    int length;
+    Py_ssize_t length;
     Py_off_t offset;
 
     if (!_PyArg_CheckPositional("pread", nargs, 3, 3)) {
@@ -4826,9 +4826,17 @@ os_pread(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
                         "integer argument expected, got float" );
         goto exit;
     }
-    length = _PyLong_AsInt(args[1]);
-    if (length == -1 && PyErr_Occurred()) {
-        goto exit;
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = PyNumber_Index(args[1]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        length = ival;
     }
     if (!Py_off_t_converter(args[2], &offset)) {
         goto exit;
@@ -8723,4 +8731,4 @@ exit:
 #ifndef OS__REMOVE_DLL_DIRECTORY_METHODDEF
     #define OS__REMOVE_DLL_DIRECTORY_METHODDEF
 #endif /* !defined(OS__REMOVE_DLL_DIRECTORY_METHODDEF) */
-/*[clinic end generated code: output=113d9fbdd18a62f5 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=799c75140d84ace5 input=a9049054013a1b77]*/

Modules/posixmodule.c

@@ -8827,11 +8827,10 @@ os_readv_impl(PyObject *module, int fd, PyObject *buffers)
 
 #ifdef HAVE_PREAD
 /*[clinic input]
-# TODO length should be size_t!  but Python doesn't support parsing size_t yet.
 os.pread
 
     fd: int
-    length: int
+    length: Py_ssize_t
     offset: Py_off_t
     /
 
@@ -8842,8 +8841,8 @@ the beginning of the file.  The file offset remains unchanged.
 [clinic start generated code]*/
 
 static PyObject *
-os_pread_impl(PyObject *module, int fd, int length, Py_off_t offset)
-/*[clinic end generated code: output=435b29ee32b54a78 input=084948dcbaa35d4c]*/
+os_pread_impl(PyObject *module, int fd, Py_ssize_t length, Py_off_t offset)
+/*[clinic end generated code: output=3f875c1eef82e32f input=85cb4a5589627144]*/
 {
     Py_ssize_t n;
     int async_err = 0;