Combining multiple for loops in Python
<p>Let's say, we have and list of objects in variable called "articles", each object has a member "tags" (which is simple list).</p>

<p>Expected output: all tags in all articles, joined in a single list.</p>

<p>In multiple lines, solution would be:</p>

<pre><code>arr = []
for article in articles:
    for tag in article.tags:
       arr.append(tag)
</code></pre>

<p>Now, how can we write this in single line instead of 4?</p>

<p>This syntax is invalid:</p>

<pre><code>arr = [tag for tag in article.tags for article in articles]
</code></pre>

<p>Thanks!</p>
