Pythonic way to create empty map of vector of vector of vector 
<p>I have the following C++ code</p>

<pre><code>std::map&lt;std::string, std::vector&lt;std::vector&lt;std::vector&lt;double&gt; &gt; &gt; &gt; details
details["string"][index][index].push_back(123.5);
</code></pre>

<p>May I know what is the Pythonic to declare an empty map of vector of vector of vector? :p</p>

<p>I try to have</p>

<pre><code>self.details = {}
self.details["string"][index][index].add(value)
</code></pre>

<p>I am getting</p>

<pre><code>KeyError: 'string'
</code></pre>
