Python in a Nutshell, 3rd Edition

Chapter 12. Time Operations

A Python program can handle time in several ways. Time intervals are floating-point numbers in units of seconds (a fraction of a second is the fractional part of the interval): all standard library functions accepting an argument that expresses a time interval in seconds accept a float as the value of that argument. Instants in time are expressed in seconds since a reference instant, known as the epoch. (Midnight, UTC, of January 1, 1970, is a popular epoch used on both Unix and Windows platforms.) Time instants often also need to be expressed as a mixture of units of measurement (e.g., years, months, days, hours, minutes, and seconds), particularly for I/O purposes. I/O, of course, also requires the ability to format times and dates into human-readable strings, and parse them back from string formats.

This chapter covers the time module, which supplies Python’s core time-handling functionality. The time module is somewhat dependent on the underlying system’s C library. The chapter also presents the datetime, sched, and calendar modules from the standard Python library, and the third-party modules dateutil and pytz.

The time Module

The underlying C library determines the range of dates that the time module can handle. On Unix systems, years 1970 and 2038 are typical cut-off points, a limitation that datetime avoids. Time instants are normally specified in UTC (Coordinated Universal Time, once known as GMT, or Greenwich Mean Time). The time module also ...