#!/usr/bin/env python

"""
Simple sample of variable name differences between Python 2.7 and Python 3.5.
"""

class PythonExpr:
    def __init__(self, expr):
        self.expr = expr = expr.strip().replace('\n', ' ')
        try:
            d = {}
            self.f_code = 'def f():\n return %s\n' % expr.strip()
            exec(self.f_code, d)
            self._f = d['f']
        except:
            raise CompilerError(('Python expression error:\n'
                                 '%s: %s') % exc_info()[:2])
    def _get_used_names(self):
        self._f_varnames = vnames = []
        for vname in self._f.__code__.co_names:
            if vname[0] not in '$_':
                vnames.append(vname)

if __name__ == '__main__':
    pe = PythonExpr('[x for x in context.assignedto if x.realname not in user_realnames]')
    pe._get_used_names()
    print(pe._f_varnames)

    # Python 2.7 displays this list:
    #   ['context', 'assignedto', 'realname', 'user_realnames']
    # Python 3.5 displays this list:
    #  ['context', 'assignedto']