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BUG: handle empty levels array in contour, closes #7486 #8719

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Merged
merged 1 commit into from
Jun 14, 2017
Merged

BUG: handle empty levels array in contour, closes #7486 #8719

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21 changes: 14 additions & 7 deletions lib/matplotlib/contour.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1132,14 +1132,10 @@ def _autolev(self, N):
self.locator = ticker.LogLocator()
else:
self.locator = ticker.MaxNLocator(N + 1, min_n_ticks=1)
zmax = self.zmax
zmin = self.zmin
lev = self.locator.tick_values(zmin, zmax)

lev = self.locator.tick_values(self.zmin, self.zmax)
self._auto = True
if self.filled:
return lev
# For line contours, drop levels outside the data range.
return lev[(lev > zmin) & (lev < zmax)]
return lev

def _contour_level_args(self, z, args):
"""
Expand All @@ -1165,6 +1161,17 @@ def _contour_level_args(self, z, args):
"Last {0} arg must give levels; see help({0})"
.format(fn))
self.levels = lev
else:
self.levels = np.asarray(self.levels).astype(np.float64)

if not self.filled:
inside = (self.levels > self.zmin) & (self.levels < self.zmax)
self.levels = self.levels[inside]
if len(self.levels) == 0:
self.levels = [self.zmin]
warnings.warn("No contour levels were found"
" within the data range.")

if self.filled and len(self.levels) < 2:
raise ValueError("Filled contours require at least 2 levels.")

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22 changes: 22 additions & 0 deletions lib/matplotlib/tests/test_contour.py
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Original file line number Diff line number Diff line change
Expand Up @@ -132,6 +132,28 @@ def test_contour_shape_invalid_2():
excinfo.match(r'Input z must be a 2D array.')


def test_contour_empty_levels():

x = np.arange(9)
z = np.random.random((9, 9))

fig, ax = plt.subplots()
with pytest.warns(UserWarning) as record:
ax.contour(x, x, z, levels=[])
assert len(record) == 1


def test_contour_uniform_z():

x = np.arange(9)
z = np.ones((9, 9))

fig, ax = plt.subplots()
with pytest.warns(UserWarning) as record:
ax.contour(x, x, z)
assert len(record) == 1


@image_comparison(baseline_images=['contour_manual_labels'])
def test_contour_manual_labels():

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