Check that a *type* of file exists in Python
<p>I realize this looks similar to other questions about checking if a file exists, but it is different. I'm trying to figure out how to check that a <strong>type</strong> of file exists and exit if it doesn't. The code I tried originally is this: </p>

<pre><code>filenames = os.listdir(os.curdir)

for filename in filenames:

   if os.path.isfile(filename) and filename.endswith('.fna'):
        ##do stuff
</code></pre>

<p>This works to 'do stuff' to the file that ends in .fna, but I need it to check and make sure the .fna file is there and exit the program entirely if not. </p>

<p>I tried this:</p>

<pre><code>try:

    if os.path.isfile(filename) and filename.endswith('.fna'):
        ## Do stuff 
except: 

    sys.stderr.write (‘No database file found. Exiting program. /n’)
    sys.exit(-1)
</code></pre>

<p>But that didn't work, it just skips the whole function if the .fna file isn't there, without printing the error.  </p>
