timelines

import datetime from timelines import timespan, timelayer

A timespan object has a start time and an end time. It can be created either by specifying a start time and an elapsed time, or by specifying both start and end times:

span1 = timespan(datetime.datetime(1984, 11, 26), datetime.timedelta(1)) span2 = timespan(datetime.datetime(1984, 11, 26) + datetime.timedelta(2), datetime.datetime(1984, 11, 26) + datetime.timedelta(2, 50)) span1.start datetime.datetime(1984, 11, 26, 0, 0) span1.elapsed datetime.timedelta(1)

The elapsed time of a timespan is the timedelta between its start and end times:

span1.elapsed == span1.end - span1.start True

A timelayer object is a sorted bag of non-overlapping timespans which know the order in which they occur:

layer = timelayer(span2, span1) list(layer) == [span1, span2] True

Just like a timespan, a timelayer knows its own start and end times:

layer.start == span1.start True layer.end == span2.end True

The elapsed duration of a timelayer is the sum of the elapsed durations of the timespans it contains, NOT the delta between its start and end times:

layer.elapsed == span1.elapsed + span2.elapsed True layer.elapsed == layer.end - layer.start False

You can add new timespans to a timelayer:

layer.start datetime.datetime(1984, 11, 26, 0, 0) layer.end datetime.datetime(1984, 11, 28, 0, 0, 50)

layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(1), datetime.timedelta(0, 600))) layer.start datetime.datetime(1984, 11, 25, 0, 0) layer.end datetime.datetime(1984, 11, 28, 0, 0, 50)

However, you cannot add new timespans which overlap any existing timespans:

layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(2), datetime.timedelta(2))) Traceback (most recent call last): ... RuntimeError: <timelayer datetime.datetime(1984, 11, 24, 0, 0) => datetime.datetime(1984, 11, 26, 0, 0) (contains 1 timespans)> overlaps <timespan datetime.datetime(1984, 11, 25, 0, 0) => datetime.datetime(1984, 11, 25, 0, 10)>

layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(1) + datetime.timedelta(0, 300), datetime.timedelta(0, 600))) Traceback (most recent call last): ... RuntimeError: <timelayer datetime.datetime(1984, 11, 25, 0, 5) => datetime.datetime(1984, 11, 25, 0, 15) (contains 1 timespans)> overlaps <timespan datetime.datetime(1984, 11, 25, 0, 0) => datetime.datetime(1984, 11, 25, 0, 10)>

layer.add(timespan(datetime.datetime(1984, 11, 26) + datetime.timedelta(0, 300), datetime.timedelta(0, 1200))) Traceback (most recent call last): ... RuntimeError: <timelayer datetime.datetime(1984, 11, 26, 0, 5) => datetime.datetime(1984, 11, 26, 0, 25) (contains 1 timespans)> overlaps <timespan datetime.datetime(1984, 11, 26, 0, 0) => datetime.datetime(1984, 11, 27, 0, 0)>

You can also add constraints to a timelayer. Constraints allow you to freeze the start time and/or end time of a timelayer, or to put an upper bound on the total elapsed time of a layer. New timespans cannot be added to a layer if they fail its constraints:

layer.freeze_start() layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(4), datetime.timedelta(2))) Traceback (most recent call last): ... RuntimeError: datetime.datetime(1984, 11, 22, 0, 0) is earlier than frozen start datetime.datetime(1984, 11, 25, 0, 0)

layer.freeze_elapsed(datetime.timedelta(3)) layer.add(timespan(datetime.datetime(1985, 11, 26), datetime.datetime(1985, 11, 29))) Traceback (most recent call last): ... RuntimeError: Total elapsed time datetime.timedelta(4, 650) is greater than frozen allowed elapsed time datetime.timedelta(3)

layer.freeze_end(datetime.datetime(1985, 11, 27)) layer.add(timespan(datetime.datetime(1985, 11, 26, 23), datetime.datetime(1985, 11, 27, 1))) Traceback (most recent call last): ... RuntimeError: datetime.datetime(1985, 11, 27, 1, 0) is later than frozen end datetime.datetime(1985, 11, 27, 0, 0)

Changelog

0.2 (2012-06-15)

• Implement timelayer.freeze_elapsed constraint, allowing the user to cap the total allowed elapsed time of a layer to a given timedelta
• Fix a bug in the guaranteed-sortedness of timelayers, by implementing timespan.cmp_
• Fix a bug in the collision detection of timelayer.add, by checking collisions against each timespan in the existing layer independently, instead of just checking against the layer's boundaries
• Exceptions during timelayer.add now provide more information about why the operation failed

0.1 (2012-06-13)

• Initial release, everything is new!