I suggest something like:
try:
os.makedirs(path)
except:
pass
open("%s/%s" % (path, filename), 'w').write(filedata)
----- Original Message -----
From: "Emile van Sebille" <em...@fenx.com>
To: <tutor@python.org>
Sent: Monday, September 13, 2010 11:56 AM
Subject: Re: [Tutor] What's the best way to ask forgiveness here?
On 9/13/2010 11:31 AM Brian Jones said...
I've been coding Python long enough that 'asking forgiveness instead of
permission' is my first instinct, but the resulting code is sometimes
clumsy, and I wonder if someone can suggest something I'm missing, or at
least validate what's going on here in some way.
What I'm trying to do is write a file to a directory. However, the
directory
may not exist the first time I try to write a file there, so I'm going to
first try to write the file, and if I get an exception, create the
directory
(er, *try* to), and *then* write the file there. Here's my first shot at
the
code:
try:
self.save_file(picfile_fullpath, picdata)
except IOError as err:
# directory doesn't exist. Try to create it.
try:
os.makedirs(picfile_fullpath)
except OSError as oserr:
logging.error("Can't create file path: %s (%s)" %
(picfile_fullpath, oserr))
else:
# Created dir, now write file.
try:
self.save_file(picfile_fullpath, picdata)
except IOError as err:
logging.error("Bailing. Couldn't save file %s (%s)"
%
(picfile_fullpath, err))
return False
Unless this is in a tight loop, I think I'd write:
try:
os.makedirs(picfile_fullpath)
try:
self.save_file(picfile_fullpath, picdata)
return True
# all/only error handling code follows.
except IOError as err:
logging.error("Bailing. Couldn't save file %s (%s)" %
(picfile_fullpath, err))
return False
except OSError as oserr:
logging.error("Can't create file path: %s (%s)" % (picfile_fullpath,
oserr))
return False
which eliminates the duplicated save_file step.
Doesn't this seem less readable than the 'ask permission' equivalent? I
think it does, but in this case asking permission for every single
operation
when the dir will only need to be created a single time (and then may be
written to several hundred times) is pretty wasteful.
Agreed -- if it's in a loop, you'd want to only check once. Of course, if
the directory is eg an nfs share, continued access could be an issue.
HTH,
Emile
I suppose I could set some sentinel variable and check for it in a while
loop, but then I need some other scaffolding code to make sure I don't
infinitely loop trying to create the directory, and probably some other
stuff I'm forgetting, so it strikes me as being just as messy.
Is there a clean sort of pattern to apply in instances like this?
Thanks.
brian
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