I think wanting to create a directory if one doesn't exist or do
nothing if it does exist and just use the existing directory is a
fairly normal programming need. Apparently this is somewhat
complicated in Python. If you use
if not os.path.exists(dirName):
os.makedirs(dirName)
you create a race condition. If you use try:
try:
os.makedirs(dirName)
except OSError:
pass
Now you're silencing too many errors, so you need to select which
errors to silence. You can check to see if the directory already
exists and assume that the directory already existing is the cause of
the error.
try:
os.makedirs(dirName)
except OSError:
if os.path.exists(dirName):
# We are nearly safe
pass
else:
# There was an error on creation, so make sure we know about
it
raise
or check the error type:
try:
os.makedirs(dirName)
except OSError, e:
if e.errno != errno.EEXIST:
raise
IMHO, os.makedirs should do this for you with something like
os.makedirs(dirName, exist = False)
and have makedirs silence the error the 'right' way whatever that is,
without turning it into an exercise for the user.
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