PR summary

This PR intends to close [ENH]: Support using datetimes as positions argument to violin(...) #30417

It should be possible to set the position of a violin plot to be a datetime. Currently, an attempt to do this results in this error message: TypeError: unsupported operand type(s) for +: 'float' and 'datetime.datetime'

The error stems from trying to perform operations between float and datetime if datetime was provided as position arguments.

The proposed solution:

• Converts datetimes in the "position" argument of a violin plot to float representation using date2num function in matplotlib.dates.
• Converts any "width" argument in the form of time difference to days.

The violinplot tests in test_axes.py were successful

An example that tests both "width" and "positions":

Example:

import datetime
import matplotlib.pyplot as plt

fig, ax = plt.subplots()
datetimes = [
    datetime.datetime(2023, 2, 10),
    datetime.datetime(2023, 5, 18),
    datetime.datetime(2023, 6, 6)
]
ax.violin(
    [
        {
            'coords': datetimes,
            'vals': [0.1, 0.5, 0.2],
            'mean': datetimes[1],
            'median': datetimes[1],
            'min': datetimes[0],
            'max': datetimes[-1],
            'quantiles': datetimes
        }
    ],
    positions=[datetime.datetime(2023, 1, 1)],
    widths=[datetime.timedelta(days=1)]
)

PR checklist

• "closes [ENH]: Support using datetimes as positions argument to violin(...) #30417" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines