Parse pip requirement file and transform it to setuptools requirements

def pip(filename):
    '''Parse pip requirement file and transform it to setuptools requirements'''
    requirements = []
    for line in open(os.path.join('requirements', filename)).readlines():
        match = RE_REQUIREMENT.match(line)
        if match:
            requirements.extend(pip(match.group('filename')))
        else:
            requirements.append(line)
    return requirements