def get_environ_vars(self, prefix='PIP_'):
        for key, val in os.environ.items():
            if key.startswith(prefix):
                yield (key.replace(prefix, '').lower(), val)
A parsed Sequence looks like [term node, OneOrMore node of
dataset/ETHPy150Open tschellenbach/Django-facebook/docs/docs_env/Lib/site-packages/pip-1.0-py2.5.egg/pip/baseparser.py/ConfigOptionParser.get_environ_vars--crossover with--dataset/ETHPy150Open erikrose/parsimonious/parsimonious/grammar.py/RuleVisitor.visit_sequence