def memory_usage():
    """return memory usage of python process in MB

    from
    http://fa.bianp.net/blog/2013/different-ways-to-get-memory-consumption-or-lessons-learned-from-memory_profiler/
    psutil is quicker

    >>> isinstance(memory_usage(),float)
    True

    """
    try:
        import psutil
        import os
    except ImportError:
        return _memory_usage_ps()

    process = psutil.Process(os.getpid())
    mem = process.memory_info()[0] / float(2 ** 20)
    return mem