python - specifically handle file exists exception

Question

I have come across examples in this forum where a specific error around files and directories is handled by testing the errno value in OSError (or IOError these days ?). For example, some discussion here - Python's "open()" throws different errors for "file not found" - how to handle both exceptions?. But, I think, that is not the right way. After all, a FileExistsError exists specifically to avoid having to worry about errno.

The following attempt didn't work as I get an error for the token FileExistsError.

try:
    os.mkdir(folderPath)
except FileExistsError:
    print 'Directory not created.'

How do you check for this and similar other errors specifically ?

Assuming you use 2.7, FileExistsError does not exist as a built-in exception in Python. See a full list of built-in exceptions here: docs.python.org/2/library/exceptions.html#module-exceptions It looks to me like you should use something like "IOError" for this. — Dyrborg
– Dyrborg, Commented Dec 26, 2013 at 20:10

falsetru · Accepted Answer · 2013-12-26 20:06:00Z

48

According to the code print ..., it seems like you're using Python 2.x. FileExistsError was added in Python 3.3; You can't use FileExistsError.

Use errno.EEXIST:

import os
import errno

try:
    os.mkdir(folderPath)
except OSError as e:
    if e.errno == errno.EEXIST:
        print('Directory not created.')
    else:
        raise

answered Dec 26, 2013 at 20:06

falsetru

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1 Comment

cogitoergosum Over a year ago

So, with Python 3.3 onwards, I can use FileExistsError. Thanks !

Tom Hale · Accepted Answer · 2019-04-19 07:03:05Z

3

Here's an example of dealing with a race condition when trying to atomically overwrite an existing symlink:

# os.symlink requires that the target does NOT exist.
# Avoid race condition of file creation between mktemp and symlink:
while True:
    temp_pathname = tempfile.mktemp()
    try:
        os.symlink(target, temp_pathname)
        break  # Success, exit loop
    except FileExistsError:
        time.sleep(0.001)  # Prevent high load in pathological conditions
    except:
        raise
os.replace(temp_pathname, link_name)

answered Apr 19, 2019 at 7:03

Tom Hale

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1 Comment

Jeronimo Over a year ago

except: raise good stuff :D

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