'Enumerate' bug correction + test case.
Transformation of (range, zip, etc...) into iterators.
* Analysis to find if it is possible to replace an expression with an iterator
* Transformation of range... into xrange...
* Tests to verify complex cases (with aliasing)
Optimization of list comprehensions :
* Transformation into map(...) if possible
* Otherwise, transformation into generator expression if possible
* All transformations include a docstring with a test case.