[Python-checkins] cpython (2.7): add example for not using access

[benjamin.peterson]

http://hg.python.org/cpython/rev/0ba50310cd9d
changeset:   70229:0ba50310cd9d
branch:      2.7
parent:      70222:6a546bf5252f
user:        Benjamin Peterson <benjamin at python.org>
date:        Fri May 20 11:41:13 2011 -0500
summary:
  add example for not using access

files:
  Doc/library/os.rst |  21 ++++++++++++++++++++-
  1 files changed, 20 insertions(+), 1 deletions(-)


diff --git a/Doc/library/os.rst b/Doc/library/os.rst
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -916,7 +916,26 @@
       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::
 

-- 
Repository URL: http://hg.python.org/cpython