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15 changes: 14 additions & 1 deletion lib/matplotlib/axes/_axes.py
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
import logging
import math
from numbers import Integral, Number
from datetime import timedelta

import numpy as np
from numpy import ma
Expand Down Expand Up @@ -3180,7 +3181,7 @@ def errorbar(self, x, y, yerr=None, xerr=None,
errors.
- *None*: No errorbar.

Note that all error arrays should have *positive* values.
Note that all error arrays should have *non-negative* values.

See :doc:`/gallery/statistics/errorbar_features`
for an example on the usage of ``xerr`` and ``yerr``.
Expand Down Expand Up @@ -3284,6 +3285,18 @@ def errorbar(self, x, y, yerr=None, xerr=None,
if len(x) != len(y):
raise ValueError("'x' and 'y' must have the same size")

def has_negative_values(array):
if array is None:
return False
try:
return np.any(array < 0)
except TypeError: # if array contains 'datetime.timedelta' types
return np.any(array < timedelta(0))

if has_negative_values(xerr) or has_negative_values(yerr):
raise ValueError(
"'xerr' and 'yerr' must have non-negative values")

if isinstance(errorevery, Integral):
errorevery = (0, errorevery)
if isinstance(errorevery, tuple):
Expand Down
19 changes: 19 additions & 0 deletions lib/matplotlib/tests/test_axes.py
Original file line number Diff line number Diff line change
Expand Up @@ -3513,6 +3513,25 @@ def test_errorbar_every_invalid():
ax.errorbar(x, y, yerr, errorevery='foobar')


def test_xerr_yerr_positive():
ax = plt.figure().subplots()

error_message = "'xerr' and 'yerr' must have non-negative values"

with pytest.raises(ValueError, match=error_message):
ax.errorbar(x=[0], y=[0], xerr=[[-0.5], [1]], yerr=[[-0.5], [1]])
with pytest.raises(ValueError, match=error_message):
ax.errorbar(x=[0], y=[0], xerr=[[-0.5], [1]])
with pytest.raises(ValueError, match=error_message):
ax.errorbar(x=[0], y=[0], yerr=[[-0.5], [1]])
with pytest.raises(ValueError, match=error_message):
x = np.arange(5)
y = [datetime.datetime(2021, 9, i * 2 + 1) for i in x]
ax.errorbar(x=x,
y=y,
yerr=datetime.timedelta(days=-10))


@check_figures_equal()
def test_errorbar_every(fig_test, fig_ref):
x = np.linspace(0, 1, 15)
Expand Down