When does python compile the constant string letters, to combine the constant strings to one constant string
<p>such as</p>

<pre><code>In [9]: dis.disassemble(compile("s = '123' + '456'", "&lt;execfile&gt;", "exec"))
  1           0 LOAD_CONST               3 ('123456')
              3 STORE_NAME               0 (s)
              6 LOAD_CONST               2 (None)
              9 RETURN_VALUE 
</code></pre>

<p>I want to know, when does python combine the constant string as the <code>CONST</code>.
If passable, please tell me which source code about this at cpython(whatever 2.x, 3.x).</p>
