How to Convert Python datetime Objects to Seconds Elapsed Since a Specific Date?

Converting datetime Objects to Seconds in Python

In Python, calculating the seconds elapsed since a fixed time in the past for a given datetime object is a common requirement. To accurately determine this duration, a few different approaches may be employed.

Special Case: January 1, 1970

For a datetime object representing January 1, 1970, there are alternative methods available for conversion to seconds:

• t.timestamp(): Returns the number of seconds since the epoch (January 1, 1970) in floating-point format.
• (t - datetime(1970, 1, 1)).total_seconds(): This calculates the difference between the given datetime object and the epoch as a timedelta object and converts it to seconds.

General Case: Any Starting Date

For a starting date other than January 1, 1970, the following steps are necessary:

1. Get the difference between the given datetime object and the desired starting date. This results in a timedelta object.
2. Use the total_seconds() method of the timedelta object to convert it to the number of seconds.

Here's an example:

import datetime
t = datetime.datetime(2009, 10, 21, 0, 0)
start_date = datetime.datetime(1985, 1, 1, 0, 0)
seconds_elapsed = (t - start_date).total_seconds()

UTC Considerations

When performing these operations, it's important to ensure that the starting date and the given datetime object are in UTC (Coordinated Universal Time). If they are not, the conversion may not be accurate. If necessary, convert the datetime objects to UTC using tzinfo attributes.

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