Two way/reverse map
<p>I'm doing this switchboard thing in python where I need to keep track of who's talking to whom, so if Alice --> Bob, then that implies that Bob --> Alice. </p>

<p>Yes, I could populate two hash maps, but I'm wondering if anyone has an idea to do it with one. </p>

<p>Or suggest another data structure.</p>

<p>There are no multiple conversations. Let's say this is for a customer service call center, so when Alice dials into the switchboard, she's only going to talk to Bob. His replies also go only to her. </p>
