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Description
Bug report
Transform functions for the new feature secondary_xaxis are always called with 0 and 1 at
instantiation, which might be invalid input for transformations.
Code for reproduction
E.g. trying to get a secondary axis showing mjd for a date axis
import matplotlib.pyplot as plt
from matplotlib.dates import date2num, num2date
from datetime import datetime, timedelta
import numpy as np
MJDREF = datetime(1858, 11, 17, 0)
def trans(mpl_date):
print(mpl_date)
return (num2date(mpl_date) - MJDREF).total_seconds() / 86400
def inv(mjd):
return date2num(MJDREF + timedelta(days=mjd))
t = np.array(['2018-01-01', '2018-03-03', '2018-04-10'], dtype='datetime64[s]')
fig, ax = plt.subplots()
ax.plot(t, [1, 2, 1])
t_ax = ax.secondary_xaxis('top', functions=(trans, inv))Results in:
ValueError: Cannot convert 0 to a date. This often happens if non-datetime values are passed to an axis that expects datetime objects.
Matplotlib version
- Operating system: linux, but should be indepenent
- Matplotlib version: 3.1
- Matplotlib backend: all
- Python version: 3.7
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