Datetime Gantt chart with milestones

broken_barh’s (start, width) spans accept a datetime-like start – handy for a real-dates Gantt chart, where plot_11_broken_barh (in the pairwise gallery) uses plain day-offsets instead. Widths stay plain numbers either way: a span’s duration, not a position, in days on a date axis. axvline and set_xlim both accept dates too, for marking a milestone and framing the visible window.

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import datetime as dt

import plotpress

fig, ax = plotpress.subplots(figsize=(9.0, 4.0))

tasks = [
    ("Design", dt.date(2024, 1, 8), 14, "#1f77b4"),
    ("Build", dt.date(2024, 1, 22), 21, "#ff7f0e"),
    ("Test", dt.date(2024, 2, 12), 10, "#2ca02c"),
    ("Launch prep", dt.date(2024, 2, 22), 7, "#d62728"),
]
for i, (name, start, days, color) in enumerate(tasks):
    ax.broken_barh([(start, days)], (i * 10, 8), color=color)

ax.set_yticks([i * 10 + 4 for i in range(len(tasks))])
ax.set_yticklabels([name for name, *_ in tasks])
ax.set_ylim(-2, len(tasks) * 10)

# A real datetime milestone marker -- axvline resolves it the same way
# plot()'s own x/y do.
ax.axvline(dt.date(2024, 2, 1), color="#333333", linestyle="--", label="Design review")
ax.legend(loc="upper left")

# set_xlim accepts ISO date strings once the axis has seen date data.
ax.set_xlim("2024-01-01", "2024-03-10")
ax.set_title("Project timeline (broken_barh with real dates)")
fig.tight_layout()