This chapter discusses the mechanics of rhythm. In part, this document’s intended audience are people who are interested in working on rhythm. However, individuals troublshooting a dependent project may also find it useful in order to illuminate whether an observed behaviour should be expected or why rhythm behaves in the observed fashion.


The primary types represented in rhythm are the range, the measure, and the point. Measures are concerned with mere deltas and Points are concerned with a position in time relative to a datum.


The hierarchy of rhythm time types is relatively straightforward, but is arguably peculiar. The Range is the base abstract class for Points and Measures. However, Points and Measures are siblings where the Point class is dependent on the presence of a Measure for Measurement operations such as rhythm.abstract.Point.measure().


In earlier versions of rhythm, Points inherited from Measures. This relationship turned out to be inappropriate as their constraints differ; the idea that a Point inherited from a Measure made it difficult to establish the semantic distinctions.

Measures are Ranges. However, their beginning is always zero, which is in direct opposition to Points whose Range begins at a relative offset with respect to the Datum. Points have a constraint as well; the end of the range is always the beginning elapsed by one unit of the representation type’s maximum precision. The Measure’s is end is always the magnitude of the measure.

Points and Measures have opposing constraints; these constraints made the earlier implementation semantically problematic as the constraint could not be inherited.


The rhythm.libunit module’s rhythm.libunit.Context class creates Point in Time types that are subclasses of the built-in Python int.

The value of the integer is an offset from the Y2K + One Day Point in Time.

The Y2K+1 datum was chosen for its nature. It’s close to the beginning of a gregorian cycle and the plus one part is used to align day units on the beginning of a week. This alignment allows common field updates to be performed with additional alignment specification.

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