python permission error

I have a file a.txt in Mac OS, which has write perms to everybody:

sh-3.2# ls -hal a.txt 
-rw-rw-rw-  1 root  wheel     0B Dec  8 11:34 a.txt
sh-3.2# pwd
/var/root

however in python it gi开发者_运维问答ves me an error:

>>> fob=open("/var/root/a.txt","w")

Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    fob=open("/var/root/a.txt","w")
IOError: [Errno 13] Permission denied: '/var/root/a.txt'

question: why?

I'm going to guess that the permissions on the /var/root directory are too strict for the user you are running as.

It's likely that you don't have write permission on the directory that the file is in.

Just a wild guess: since the file already exists there, is it possible that opening with mode "w+" or "r+" instead of "w" allows you to write to the file?

I don't have an OS X computer available, and it's most probable that it's an issue of the directory permissions, however I'd try the mode change, just in case.