Vertical or horizontal bar

The pygmt.Figure.plot method can plot vertical (b) or horizontal (B) bars by passing the corresponding shortcut to the style parameter.

Out:

<IPython.core.display.Image object>

import pygmt

fig = pygmt.Figure()

with fig.subplot(
    nrows=1, ncols=2, subsize=("8c", "4c"), frame=["ag", "WSne"], sharey=True
):

    fig.basemap(region=[0, 4, 0, 3], panel=True, frame="+tvertical")
    fig.basemap(region=[0, 4, 0, 3], panel=True, frame="+thorizontal")

    pen = "1.5p"
    with fig.set_panel(panel=0):
        color = "skyblue"
        fig.plot(x=1, y=2, style="b0.5c", color=color, pen=pen)
        fig.plot(x=2, y=2.5, style="b1c", color=color, pen=pen)
        fig.plot(x=3, y=2.5, style="b0.75c+b1", color=color, pen=pen)

    with fig.set_panel(panel=1):
        color = "tomato"
        fig.plot(x=1.5, y=0.5, style="B0.75c", color=color, pen=pen)
        fig.plot(x=3, y=1.5, style="B1c", color=color, pen=pen)
        fig.plot(x=3.5, y=2.5, style="B0.5c+b2", color=color, pen=pen)

fig.show()