add example for not using access

benjaminp · benjaminp · commit 249b508c98d9 · 2011-05-20T11:41:13.000-05:00
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
@@ -772,7 +772,26 @@ Files and Directories
       Using :func:`access` to check if a user is authorized to e.g. open a file
       before actually doing so using :func:`open` creates a security hole,
       because the user might exploit the short time interval between checking
-      and opening the file to manipulate it.
+      and opening the file to manipulate it. It's preferable to use :term:`EAFP`
+      techniques. For example::
+
+         if os.access("myfile", os.R_OK):
+             with open("myfile") as fp:
+                 return fp.read()
+         return "some default data"
+
+      is better written as::
+
+         try:
+             fp = open("myfile")
+         except OSError as e:
+             if e.errno == errno.EACCESS:
+                 return "some default data"
+             # Not a permission error.
+             raise
+         else:
+             with fp:
+                 return fp.read()
 
    .. note::
 
