title: Python AST: several semantics unclear, e.g. expr_context
body: <p>Is there any more than the <a href="http://docs.python.org/library/ast.html" rel="nofollow"><code>ast</code> documentation</a> about the <code>ast</code> module?</p>
  
  <p>Esp., I am wondering what <code>expr_context</code> (and all its possible values) exactly means.</p>
  
  <p>Also, what is the difference between <code>Assign</code> and <code>AugAssign</code>?</p>
  
  <p>Also, it is possible to reference to a real Python object instead of its name when doing an assignment to a local variable? I am building an AST myself and I have some Python objects which I want to access to in the AST. The alternative would be to introduce some dummy temp var name for them and add that dummy var name to the <code>globals()</code> scope for the later compiled function but that seems somewhat bad (slow and hacky) to me.</p>