Timing context manager

timing.py

@contextmanager
def timing(label=None, time_func=simulator.timestamp):
    """
    Can be used in conjunction with ``with`` statement to easily measure duration.
    Args:
        time_func:
        label: represents the measurement

    Returns:
        A callable. Once invoked will return one of the following (duration in seconds):
        1. A tuple of ``label`` and duration, f ``label`` is not ``None``
        2. Otherwise, returns the duration

    Example:
        >>> import math
        >>> import time
        >>> with timing('foo') as duration:  # test timing with label
        ...     time.sleep(1.3)
        ...
        >>> d = duration()
        >>> d[0]
        'foo'
        >>> round(math.fabs(d[1]-1.3), 2)
        0.0
        >>> with timing() as duration:  # test timing without label
        ...     time.sleep(0.4)
        ...
        >>> round(math.fabs(duration()-0.4), 2)
        0.0
    """
    t0 = time_func()
    yield lambda: (label, t1 - t0) if label is not None else (t1 - t0)
    t1 = time_func()