Hello all, The following is a copy of a blog entry. It's asking a question about future statements and the built in compile function. I'd appreciate any pointers or comments about possible approaches.
`Movable Python <http://www.voidspace.org.uk/python/movpy/>`_ supports running both Python scripts and ``.pyc`` bytecode files. It does this by compiling scripts to bytecode, or extracting the code object from bytecode files, and then calling ``exec``. When you call `compile <http://docs.python.org/dev/lib/built-in-funcs.html>`_ you can pass in an optional ``flags`` argument which tell Python which future statements to compile the code with. I currently don't do this, which means that ``from __future__ import ...`` statements are ignored. For Python 2.4.2 the most significant of these is `division <http://www.python.org/doc/peps/pep-0238/>`_. Code which expects integer division to yield floats is just plain broken if this future statement is ignored. I'd like to fix this in the next release of **Movable Python**. First of all, I *assume* that the code objects contained in bytecode files are already compiled with the relevant future statements. This would mean that no further action is necessary. Can anyone confirm if this is correct ? [#]_ For Python scripts there are a couple of possible approaches. The simplest approach would be to use a simple regular expression to find statements that look like ``from __future__ ...``. Unfortunately this could score false positives for comments and docstrings. [#]_ Another alternative would be to parse the code into an abstract syntax tree using the `compiler module <http://docs.python.org/lib/module-compiler.html>`_. I would then have to recognise the import statements in the nodes. I can see that there is an `Import node <http://docs.python.org/lib/module-compiler.ast.html>`_ does anyone have any hints for me with this approach ? I would prefer a solution that works across Python versions 2.2 to 2.5 and beyond. Ominously, the ``compile.compile`` function has unsupported options for passing in ``flags``, so it looks like it doesn't handle it automatically from the parse tree. .. [#] It will actually be easy enough to test. .. [#] Future statements shuld only occur at the toplevel of code, and in fact ought to occur before any other statements (although that was broken in Python 2.4), so it ought to be possible to minimize false positives a bit. -- http://mail.python.org/mailman/listinfo/python-list
