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Simple Date classes

The official datetime module is fully featured but substantial. This Date class has no concept of time, but is very compact. Dates are stored as a small int. Contrary to normal MP practice, properties are used. This allows basic arithmetic syntax while ensuring automatic rollover. The speed penalty of properties is unlikely to be a factor in date operations.

The Date class provides basic arithmetic and comparison methods. The DateCal subclass adds pretty printing and methods to assist in creating calendars.

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Date class

The Date class embodies a single date value which may be modified, copied and compared with other Date instances.

Constructor

This takes a single optional arg:

  • lt=None By default the date is initialised from system time. To set the date from another time source, a valid localtime/gmtime tuple may be passed.

Method

  • now Arg lt=None. Sets the instance to the current date, from system time or lt as described above.

Writeable properties

  • year e.g. 2023.
  • month 1 == January. May be set to any number, years will roll over if necessary. e.g. d.month += 15 or d.month -= 1.
  • mday Adjust day in current month. Allowed range 1..month_length.
  • day Days since epoch. Note that the epoch varies with platform - the value may be treated as an opaque small integer. Use to adjust a date with rollover (d.day += 7) or to assign one date to another (date2.day = date1.day). May also be used to represnt a date as a small int for saving to a file.

Read-only property

  • wday Day of week. 0==Monday 6==Sunday.

Date comparisons

Python "magic methods" enable date comparisons using standard operators <, <=, >, >=, ==, !=.

DateCal class

This adds pretty formatting and functionality to return additional information about the current date. The added methods and properties do not change the date value. Primarily intended for calendars.

Constructor

This takes a single optional arg:

  • lt=None See Date constructor.

Methods

  • time_offset arg hr=6. This returns 0 or 1, being the offset in hours of UK local time to UTC. By default the change occurs when the date changes at 00:00 UTC on the last Sunday in March and October. If an hour value is passed, the change will occur at the correct 01:00 UTC. This method will need to be adapted for other geographic locations.
  • wday_n arg mday=1. Return the weekday for a given day of the month.
  • mday_list arg wday. Given a weekday, for the current month return an ordered list of month days matching that weekday.

Read-only properties

  • month_length Length of month in days.
  • day_str Day of week as a string, e.g. "Wednesday".
  • month_str Month as a string, e.g. "August".

Class variables

  • days A 7-tuple ("Monday", "Tuesday"...)
  • months A 12-tuple ("January", "February",...)

Example usage

from date import Date
d = Date()
d.month = 1  # Set to January
d.month -= 2  # Date changes to same mday in November previous year.
d.mday = 25  # Set absolute day of month
d.day += 7  # Advance date by one week. Month/year rollover is handled.
today = Date()
if d == today:  # Date comparisons
    # do something
new_date = Date()
new_date.day = d.day  # Assign d to new_date: now new_date == d.
print(d)  # Basic numeric print.

The DateCal class:

from date import DateCal
d = DateCal()
# Correct a UK clock for DST
d.now()
hour = (hour_utc + d.time_offset(hour_utc)) % 24
print(d)  # Pretty print
x = d.wday_n(1)  # Get day of week of 1st day of month
sundays = d.mday_list(6)  # List Sundays for the month.
wday_last = d.wday_n(d.month_length)  # Weekday of last day of month