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