def timestamp_to_float(time):
    """Convert a pandas timestamp to a floating point date.

    >>> import datetime
    >>> time = datetime.date(2010, 10, 1)
    >>> timestamp_to_float(time)
    2010.75
    >>> time = datetime.date(2011, 4, 1)
    >>> timestamp_to_float(time)
    2011.25
    >>> timestamp_to_float(datetime.date(2011, 1, 1))
    2011.0
    >>> timestamp_to_float(datetime.date(2011, 12, 1)) == (2011.0 + 11.0 / 12)
    True
    """
    return time.year + (time.month - 1) / 12.0
