How can I safely create a nested directory?

Asked : Nov 17

Viewed : 20 times

What is the most elegant way to check if the directory a file is going to be written to exists, and if not, create the directory using Python? Here is what I tried:

import os

file_path = "/my/directory/filename.txt"
directory = os.path.dirname(file_path)

try:
    os.stat(directory)
except:
    os.mkdir(directory)

f = file(filename)

Somehow, I missed os.path.exists (thanks kanja, Blair, and Douglas). This is what I have now:

def ensure_dir(file_path):
    directory = os.path.dirname(file_path)
    if not os.path.exists(directory):
        os.makedirs(directory)

Is there a flag for open(), that make this happen automatically?

python exception path directory operating-system 

Nov 17

4 Answers

On Python ≥ 3.5, use pathlib.Path.mkdir:

from pathlib import Path
Path("/my/directory").mkdir(parents=True, exist_ok=True)

For older versions of Python, I see two answers with good qualities, each with a small flaw, so I will give my take on it:

Try os.path.exists, and consider os.makedirs for the creation.

import os
if not os.path.exists(directory):
    os.makedirs(directory)

As noted in comments and elsewhere, there's a race condition – if the directory is created between the os.path.exists and the os.makedirs calls, the os.makedirs will fail with an OSError. Unfortunately, blanket-catching OSError and continuing is not foolproof, as it will ignore a failure to create the directory due to other factors, such as insufficient permissions, full disk, etc.

One option would be to trap the OSError and examine the embedded error code (see Is there a cross-platform way of getting information from Python’s OSError):

import os, errno

try:
    os.makedirs(directory)
except OSError as e:
    if e.errno != errno.EEXIST:
        raise

Alternatively, there could be a second os.path.exists, but suppose another created the directory after the first check, then removed it before the second one – we could still be fooled.

Depending on the application, the danger of concurrent operations may be more or less than the danger posed by other factors such as file permissions. The developer would have to know more about the particular application being developed and its expected environment before choosing an implementation.

Modern versions of Python improve this code quite a bit, both by exposing FileExistsError (in 3.3+)...

try:
    os.makedirs("path/to/directory")
except FileExistsError:
    # directory already exists
    pass

...and by allowing a keyword argument to os.makedirs called exist_ok (in 3.2+).

os.makedirs("path/to/directory", exist_ok=True)  # succeeds even if directory exists.

answered Jan 18


Check os.makedirs: (It makes sure the complete path exists.)
To handle the fact the directory might exist, catch OSError. (If exist_ok is False (the default), an OSError is raised if the target directory already exists.)

import os
try:
    os.makedirs('./path/to/somewhere')
except OSError:
    pass

answered Jan 18


we want to bundle everything together into a tidy function we can do so as follows:

def makeDirectory(path_to_directory):
   p = Path(path_to_directory)
   p.mkdir(exists_ok=True, parents=True)

answered Jan 18


To safely create a nested directory in Python, we can use the Path instance’s mkdir method.

For instance, we write:

from pathlib import Path
Path("./my/directory").mkdir(parents=True, exist_ok=True)

We invoke the Path constructor with the path of the directory we want to create.

Then we set parents and exist_ok to True so that it’ll create the nested directory without the parent directory being present.

answered Jan 18


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