title: Where can I find source code of modules in `lib-dynload`?
body: <p>Many built-in libraries use C implementations whenever possible.</p>
  
  <p>For example, <code>heapq</code> uses <code>lib-dynload/_heapq.so</code> if it's available.</p>
  
  <p>Where can I find source code of modules like <code>_heapq</code>?</p>