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copied!<p>If you'd like to access a string 3 characters at a time, you're going to need to use <a href="https://stackoverflow.com/a/509295/600110">slicing</a>.</p> <p>You can get a list of the 3-character long pieces of the string using a list comprehension like this:</p> <pre><code>>>> x = 'this is a string' >>> step = 3 >>> [x[i:i+step] for i in range(0, len(x), step)] ['thi', 's i', 's a', ' st', 'rin', 'g'] >>> step = 5 >>> [x[i:i+step] for i in range(0, len(x), step)] ['this ', 'is a ', 'strin', 'g'] </code></pre> <p>The important bit is:</p> <pre><code>[x[i:i+step] for i in range(0, len(x), step)] </code></pre> <p><code>range(0, len(x), step)</code> gets us the indices of the start of each <code>step</code>-character slice. <code>for i in</code> will iterate over these indices. <code>x[i:i+step]</code> gets the slice of <code>x</code> that starts at the index <code>i</code> and is <code>step</code> characters long.</p> <p>If you know that you will get <em>exactly</em> four pieces every time, then you can do:</p> <pre><code>a, b, c, d = [x[i:i+step] for i in range(0, len(x), step)] </code></pre> <p>This will happen if <code>3 * step < len(x) <= 4 * step</code>.</p> <p>If you don't have exactly four pieces, then Python will give you a <code>ValueError</code> trying to unpack this list. Because of this, I would consider this technique very brittle, and would not use it.</p> <p>You can simply do</p> <pre><code>x_pieces = [x[i:i+step] for i in range(0, len(x), step)] </code></pre> <p>Now, where you used to access <code>a</code>, you can access <code>x_pieces[0]</code>. For <code>b</code>, you can use <code>x_pieces[1]</code> and so on. This allows you much more flexibility.</p>

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