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    <p>I see two answers with good qualities, each with a small flaw, so I will give my take on it:</p> <p>Try <a href="https://docs.python.org/2/library/os.path.html#os.path.exists" rel="noreferrer"><code>os.path.exists</code></a>, and consider <a href="https://docs.python.org/2/library/os.html#os.makedirs" rel="noreferrer"><code>os.makedirs</code></a> for the creation.</p> <pre><code>import os if not os.path.exists(directory): os.makedirs(directory) </code></pre> <p>As noted in comments and elsewhere, there's a race condition - if the directory is created between the <code>os.path.exists</code> and the <code>os.makedirs</code> calls, the <code>os.makedirs</code> will fail with an <code>OSError</code>. Unfortunately, blanket-catching <code>OSError</code> 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.</p> <p>One option would be to trap the <code>OSError</code> and examine the embedded error code (see <a href="https://stackoverflow.com/questions/273698/is-there-a-cross-platform-way-of-getting-information-from-pythons-oserror">Is there a cross-platform way of getting information from Python’s OSError</a>):</p> <pre><code>import os, errno try: os.makedirs(directory) except OSError as e: if e.errno != errno.EEXIST: raise </code></pre> <p>Alternatively, there could be a second <code>os.path.exists</code>, but suppose another created the directory after the first check, then removed it before the second one - we could still be fooled. </p> <p>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.</p>
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    1. POHow can I safely create a nested directory in Python?
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    1. USDan Ciborowski - MSFT
    1. USBlair Conrad
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    1. POHow can I safely create a nested directory in Python?
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    1. COagreed the try/except solution is better
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      1. USCorey Goldberg
    2. COThe race condition is a good point, but the approach in http://stackoverflow.com/questions/273192/#273208, will mask a failure to create the directory. Don't feel bad for voting down - you don't like the answer. It's what votes are for.
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      1. USBlair Conrad
    3. CORemember that os.path.exists() isn't free. If the normal case is that the directory will be there, then the case where it isn't should be handled as an exception. In other words, try to open and write to your file, catch the OSError exception and, based on errno, do your makedir() and re-try or re-raise. This creates duplication of code unless you wrap the writing in a local method.
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      1. USAndrew
 

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