That's a tough one, in general. First, here are a list of things to
remember before diving further:
-* Performance characteristics vary accross Python implementations. This FAQ
+* Performance characteristics vary across Python implementations. This FAQ
focusses on :term:`CPython`.
-* Behaviour can vary accross operating systems, especially when talking about
+* Behaviour can vary across operating systems, especially when talking about
I/O or multi-threading.
* You should always find the hot spots in your program *before* attempting to
optimize any code (see the :mod:`profile` module).