Python: Elementwise join of two lists of same length
<p>I have two lists of the same length </p>

<pre><code>a = [[1,2], [2,3], [3,4]]
b = [[9], [10,11], [12,13,19,20]]
</code></pre>

<p>and want to combine them to</p>

<pre><code>c = [[1, 2, 9], [2, 3, 10, 11], [3, 4, 12, 13, 19, 20]]
</code></pre>

<p>I do this by</p>

<pre><code>c= []
for i in range(0,len(a)):
    c.append(a[i]+ b[i])
</code></pre>

<p>However, I am used from R to avoid for loops and the alternatives like zip and itertools do not generate my desired output. Is there a way to do it better? </p>

<p><strong>EDIT:</strong> 
Thanks for the help! My lists have 300,000 components. The execution time of the solutions are</p>

<pre><code>[a_ + b_ for a_, b_ in zip(a, b)] 
1.59425 seconds
list(map(operator.add, a, b))
2.11901 seconds
</code></pre>