I wrote this function is my program:

def timedelta2seconds(delta):
    """
    Convert a datetime.timedelta() objet to a number of second
    (floatting point number).

    >>> timedelta2seconds(timedelta(seconds=2, microseconds=40000))
    2.04
    >>> timedelta2seconds(timedelta(minutes=1, milliseconds=250))
    60.25
    """
    return delta.microseconds / 1000000.0 \
        + delta.seconds + delta.days * 60*60*24

About the use cases: I use it to compute the compression rate of an 
audio song (bytes / seconds), to compute the bit rate of a video 
(bytes / seconds). I'm using datetime.timedelta() to store the 
audio/video duration.

It's not related to time_t: see issue #2736 for 
datetime.datetime.totimestamp(). And about time_t: I don't about 31 
bits signed integer. It's not beacuse other programs have arbitrary 
limits than Python should also be limited.

About the patch: I don't like the name "tosecs", it's not consistent 
with the constructor: timedelta(seconds=...).tosec[ond]s(). And why 
dropping the microseconds? For short duration, microseconds are 
useful.