[FIXED] Invisible major grid line hides visible minor grid lines

Issue

I'm trying to plot some data against dates and I ran into a problem regarding the grid. I want on the x-axis the dates, with the major ticks for the months and the minor ticks for the weeks. However for the grid, I only want to see the minor ones. When building the plot, I noticed there is a part of the grid missing for November:

Here's the minimal example that reproduces the above problem.

from datetime import datetime

import matplotlib as mpl
from matplotlib import pyplot as plt
from matplotlib import dates as mdates


fig, ax = plt.subplots()

ax.xaxis.set_minor_locator(mdates.WeekdayLocator(byweekday=mdates.MO))
ax.xaxis.set_major_locator(mdates.MonthLocator())
ax.xaxis.set_major_formatter(
    mdates.ConciseDateFormatter(mdates.AutoDateLocator())
)

ax.set_xlim(datetime(2021, 9, 1), datetime(2022, 1, 1))

ax.xaxis.grid(color="gray", linestyle="dashed", alpha=0.2, which="minor")

plt.show()

I assume it is because the invisible major line which overlapping with the minor line that should be plotted. Can anyone explain what is going on and how to fix this?

Solution

The reason is that minor tick lines are shown at minor tick positions and that minor ticks are suppressed if they coincide with a major tick position.

This behavior can be controlled by remove_overlapping_locs.

Setting

ax.xaxis.remove_overlapping_locs = False

results in

Answered By - Stef