number of zeroes to prefix file number
<p>The point of this is to find number of zeroes to put in new file names.
Say, if there is 86 files in dir, we need to start file names from 00 (or 01), if there's 600, 001, etc.</p>

<pre><code>dir_ls = os.listdir(os.getcwd())

# number of zeroes to prefix file number
ln = len(str(len(dir_ls))) - 1
</code></pre>

<p>Is it all right, or this can be done better?
This double conversion feels stupid.</p>
