import datetime

import numpy as np
import matplotlib.pyplot as plt


# Sample data for contour plot
dates = [datetime.datetime(2023, 10, 1) + datetime.timedelta(days=i) for i in range(10)]
x_start, x_end, x_step = -10.0, 5.0, 0.5
y_start, y_end, y_step = 0, 10, 1

x = np.arange(x_start, x_end, x_step)
y = np.arange(y_start, y_end, y_step)

# In this case, Y axis has dates
X, Y = np.meshgrid(x, dates)

rows = len(X)
cols = len(X[0])

z1D = np.arange(rows * cols)
Z = z1D.reshape((rows, cols))

fig, ax = plt.subplots()
CS = ax.contour(X, Y, Z)

ax.clabel(CS, CS.levels, inline=True, fmt=dict(zip(CS.levels, dates)),
          manual=[(x, y) for x, y in zip(x, dates)])

Traceback (most recent call last):
  File "/home/elliott/code/matplotlib/clabel.py", line 27, in <module>
    ax.clabel(CS, CS.levels, inline=True, fmt=dict(zip(CS.levels, dates)),
  File "/home/elliott/code/matplotlib/lib/matplotlib/axes/_axes.py", line 6581, in clabel
    return CS.clabel(levels, **kwargs)
  File "/home/elliott/code/matplotlib/lib/matplotlib/contour.py", line 195, in clabel
    self.add_label_near(x, y, inline, inline_spacing)
  File "/home/elliott/code/matplotlib/lib/matplotlib/contour.py", line 553, in add_label_near
    x, y = transform.transform((x, y))
  File "/home/elliott/code/matplotlib/lib/matplotlib/transforms.py", line 1508, in transform
    res = self.transform_affine(self.transform_non_affine(values))
  File "/home/elliott/code/matplotlib/lib/matplotlib/_api/deprecation.py", line 297, in wrapper
    return func(*args, **kwargs)
  File "/home/elliott/code/matplotlib/lib/matplotlib/transforms.py", line 2422, in transform_affine
    return self.get_affine().transform(values)
  File "/home/elliott/code/matplotlib/lib/matplotlib/transforms.py", line 1797, in transform
    return self.transform_affine(values)
  File "/home/elliott/code/matplotlib/lib/matplotlib/_api/deprecation.py", line 297, in wrapper
    return func(*args, **kwargs)
  File "/home/elliott/code/matplotlib/lib/matplotlib/transforms.py", line 1868, in transform_affine
    return affine_transform(values, mtx)
TypeError: Cannot cast array data from dtype('O') to dtype('float64') according to the rule 'safe'