epoch before Python 3.3

Converting datetime object to the number of seconds since the start of the epoch is not a simple task until Python 3.3.

The most natural solution for the problem is to use strftime method that can format the datetime. Using %s as a format you can get a timestamp. Look at the example:

naive_time = datetime(2018, 3, 31, 12, 0, 0)
utc_time = pytz.utc.localize(naive_time)
ny_time = utc_time.astimezone(
    pytz.timezone('US/Eastern'))

ny_time is the exact the same moment as utc_time, but written as New Yorkers see it:

# utc_time
datetime.datetime(2018, 3, 31, 12, 0,
    tzinfo=<UTC>)
# ny_time
datetime.datetime(2018, 3, 31, 8, 0,
    tzinfo=<DstTzInfo 'US/Eastern' ...>)

Since they are the same moments, their timestamps should be equal:

In : int(utc_time.strftime('%s')),
     int(ny_time.strftime('%s'))
Out: (1522486800, 1522468800)

Wait, what? They are not the same at all. In fact, you can't use strftime as a solution for this problem. Python's strftime doesn't even support %s as an argument, it merely works because internally the platform C library’s strftime() is called. But, as you can see, the timezone of datetime object is wholly ignored.

The proper result can be achieved with straightforward subtraction:

In : epoch_start = pytz.utc.localize(datetime(1970, 1, 1))

In : (utc_time - epoch_start).total_seconds()
Out: 1522497600.0

In : (utc_time - epoch_start).total_seconds()
Out: 1522497600.0

Again, if you use Python 3.3+, you can solve the problem with timestamp() method of datetime: utc_time.timestamp().