Overview

pyTooling.Diagram describes diagrams; it doesn’t draw them. A diagram is a small data model - what the picture is - and a renderer turns that model into a picture with whatever library is at hand. Producers and renderers therefore don’t have to know each other: a producer builds the model its own data implies, and every renderer draws the same model.

Gantt Charts

pyTooling.Diagram.Gantt describes a Gantt chart: rows of bars on a time scale.

from datetime import datetime, timedelta
from pyTooling.Diagram.Gantt import Diagram, Row, Bar

begin =   datetime(2026, 9, 15, 8, 0)
diagram = Diagram("Nightly build", begin)

compile = Row("Compile", parent=diagram)
Bar(begin + timedelta(minutes=1), begin + timedelta(minutes=5), parent=compile)

test = Row("Test", parent=diagram)
Bar(begin + timedelta(minutes=5), begin + timedelta(minutes=21), parent=test)

Three classes, each one containing the next:

Class	Is
`Diagram`	the chart: its title, its origin and its rows.
`Row`	the bars drawn on one line, under one name.
`Bar`	a time range within a row.

An element is created with its parent and appends itself to it, so the model is built top down and is never half-attached. Every element knows the diagram it belongs to - Diagram - so reaching the origin from a bar costs no walk.

Three ways to ask where a bar is

A chart is drawn on offsets, a report usually wants times, and a comparison within a row wants neither, so a bar answers all three:

Property	Answers
`Begin`, `End`	the times themselves, as `datetime`.
`BeginSinceOrigin`, `EndSinceOrigin`	the distance from the diagram’s origin, as `timedelta`.
`BeginSinceParent`, `EndSinceParent`	the distance from the row’s begin, which is zero for the row’s earliest bar.
`Duration`	the bar’s own length.

A distance is a timedelta, because that is what subtracting two times yields. Where a drawing library wants a number, the ***InSeconds properties - BeginSinceOriginInSeconds, EndSinceOriginInSeconds and DurationInSeconds - hand out float seconds instead.

Hint

The origin is stated, not derived. The scale a chart is drawn on usually begins before its first bar - a pipeline starts before its first job does - so Diagram takes the origin as a parameter rather than taking the earliest bar’s begin.

A row spans its bars: it begins with its earliest and ends with its latest, gaps between them included. A row without bars has neither, and asking raises a DiagramError rather than answering with None.

Building one from your own data

A producer derives from the three classes and adds what its domain knows. GanttLayout does exactly that for a software execution trace: its rows carry the timespan they show and its depth in the trace’s tree, and its bars carry whether a job was waiting for a runner and whether it is still running. See Rendering.