Support expand_from_start_time

[mghextreme]

Issue

When unsing the library, we wanted to generate dates using the cron on a repeat (e.g. every 7 days with cron 0 0 */7 * *), but, even though we set the start_time, the library just uses preset values to generate the possible dates.

Code

A new parameter was added when creating a croniter instance - expand_from_start_time. When True, the expnaded values will be generated based on the start_time date set when creating the instance.

Current behavior

0 0 */7 * *, start time today (2024-07-11): get_next() would generate 2024-07-15 (4 days from now) ❌

New behavior

0 0 */7 * *, start time today (2024-07-11): get_next() would generate 2024-07-18 (7 days from now) ✅

Only if the new parameter is set to True

Important

Because the expanded values are generated when creating the croniter instance, using expand_from_start_time=True and setting start_time on the get_next() method is not supported.

Changes

I made the initial changes, but wanted the opinion of the mantainers before moving forward with the changes.

• Support new feature
• Added unit tests
• Edge case support (expanded values for when the next goes over the max value - or prev goes under the min)
• Documentation

[kiorky]

I do not reproduce your bug.

>>> iter = croniter.croniter('0 0 */7 * *', datetime.datetime(2024,3,3)); pprint([iter.get_next(datetime.datetime) for i in range(3)])
[datetime.datetime(2024, 3, 8, 0, 0),
datetime.datetime(2024, 3, 15, 0, 0),
datetime.datetime(2024, 3, 22, 0, 0)]

[kiorky]

(and even with currentDate+afewdays)

>>> iter = croniter.croniter('0 0 */7 * *', datetime.datetime.now()); pprint([iter.get_next(datetime.datetime) for i in range(3)])
[datetime.datetime(2024, 7, 15, 0, 0),
 datetime.datetime(2024, 7, 22, 0, 0),
 datetime.datetime(2024, 7, 29, 0, 0)]
>>> iter = croniter.croniter('0 0 */7 * *', datetime.datetime.now()+datetime.timedelta(days=4)); pprint([iter.get_next(datetime.datetime) for i in range(3)])
[datetime.datetime(2024, 7, 22, 0, 0),
 datetime.datetime(2024, 7, 29, 0, 0),
 datetime.datetime(2024, 8, 1, 0, 0)]

[mghextreme]

I do not reproduce your bug.

>>> iter = croniter.croniter('0 0 */7 * *', datetime.datetime(2024,3,3)); pprint([iter.get_next(datetime.datetime) for i in range(3)])
[datetime.datetime(2024, 3, 8, 0, 0),
datetime.datetime(2024, 3, 15, 0, 0),
datetime.datetime(2024, 3, 22, 0, 0)]

What I'm proposing it's not a bugfix.

In your example, you use the cron '0 0 */7 * *', means every 7 days.
But, by setting start_time as 2024-03-03, the next generated time is 2024-03-08 (5 days later, not 7).

By using the parameter I proposed it would still consider a 7 day gap. So instead of 2024-03-08 it would return 2024-03-10 (7 days later, same interval as the cron string).

[kiorky]

Ok, i better understand.
Why not, but please remove typing and non py2 compatible code as i still want to maintain this compat.

[kiorky]

i manually merged your commits and made the neccessary changes, thx !

[kiorky]

released as 2.0.6