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Warn on redundant definition of plot properties #19277

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Merged
merged 1 commit into from
Jan 13, 2021
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Warn on redundant definition of plot properties #19277

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2 changes: 1 addition & 1 deletion examples/misc/svg_filter_line.py
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Expand Up @@ -20,7 +20,7 @@
l1, = ax.plot([0.1, 0.5, 0.9], [0.1, 0.9, 0.5], "bo-",
mec="b", lw=5, ms=10, label="Line 1")
l2, = ax.plot([0.1, 0.5, 0.9], [0.5, 0.2, 0.7], "rs-",
mec="r", lw=5, ms=10, color="r", label="Line 2")
mec="r", lw=5, ms=10, label="Line 2")


for l in [l1, l2]:
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26 changes: 24 additions & 2 deletions lib/matplotlib/axes/_base.py
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Expand Up @@ -117,6 +117,9 @@ def __call__(self, ax, renderer):
self._transform - ax.figure.transSubfigure)


_FORMAT_UNSET = 'None'
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should that not have been an object() placeholder, to avoid confusion with other meanings of the string "none"?

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@timhoffm timhoffm Jan 14, 2021 •
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@anntzer When linestyle or marker are not specified in a format string, they are deactivated. "None" actually serves as value down the road in set_linestyle(). We cannot have a proper sentinel (or would have to convert it again down the road).

My intention was to make it more clear what the semantics of the value are. Otherwise

matplotlib/lib/matplotlib/axes/_base.py

Line 474 in 2219872

and val != _FORMAT_UNSET):

would be and val != 'None'. Which is less understandable, and freaks me out because of the case-insensitivity of our 'none' string handling. I was about to write and val.lower() != 'none' since I didn't follow closely where that was coming from, but then again, val can be a 4-tuple for colors, which you cannot lower().

But thinking again, it's better to be explicit with 'none' and not pretend to have a sentinel, that actually has hidden meaning. See #19291.

Edit: It's not that "simple" 🙄 . #19291 fails a number of tests.

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thanks for taking care of that.



def _process_plot_format(fmt):
"""
Convert a MATLAB style color/line style format string to a (*linestyle*,
Expand All @@ -129,6 +132,10 @@ def _process_plot_format(fmt):
* 'r--': red dashed lines
* 'C2--': the third color in the color cycle, dashed lines

The format is absolute in the sense that if a linestyle or marker is not
defined in *fmt*, there is no line or marker. This is expressed by
returning _FORMAT_UNSET for the respective quantity.

See Also
--------
matplotlib.Line2D.lineStyles, matplotlib.colors.cnames
Expand Down Expand Up @@ -196,9 +203,9 @@ def _process_plot_format(fmt):
if linestyle is None and marker is None:
linestyle = mpl.rcParams['lines.linestyle']
if linestyle is None:
linestyle = 'None'
linestyle = _FORMAT_UNSET
if marker is None:
marker = 'None'
marker = _FORMAT_UNSET

return linestyle, marker, color

Expand Down Expand Up @@ -461,6 +468,21 @@ def _plot_args(self, tup, kwargs, return_kwargs=False):
for prop_name, val in zip(('linestyle', 'marker', 'color'),
(linestyle, marker, color)):
if val is not None:
# check for conflicts between fmt and kwargs
if (fmt.lower() != 'none'
and prop_name in kwargs
and val != _FORMAT_UNSET):
# Technically ``plot(x, y, 'o', ls='--')`` is a conflict
# because 'o' implicitly unsets the linestyle
# (linestyle=_FORMAT_UNSET).
# We'll gracefully not warn in this case because an
# explicit set via kwargs can be seen as intention to
# override an implicit unset.
_api.warn_external(
f"{prop_name} is redundantly defined by the "
f"'{prop_name}' keyword argument and the fmt string "
f'"{fmt}" (-> {prop_name}={val!r}). The keyword '
f"argument will take precedence.")
kw[prop_name] = val

if len(xy) == 2:
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11 changes: 11 additions & 0 deletions lib/matplotlib/tests/test_axes.py
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Expand Up @@ -624,6 +624,17 @@ def test_fill_units():
fig.autofmt_xdate()


def test_plot_format_kwarg_redundant():
with pytest.warns(UserWarning, match="marker .* redundantly defined"):
plt.plot([0], [0], 'o', marker='x')
with pytest.warns(UserWarning, match="linestyle .* redundantly defined"):
plt.plot([0], [0], '-', linestyle='--')
with pytest.warns(UserWarning, match="color .* redundantly defined"):
plt.plot([0], [0], 'r', color='blue')
# smoke-test: should not warn
plt.errorbar([0], [0], fmt='none', color='blue')


@image_comparison(['single_point', 'single_point'])
def test_single_point():
# Issue #1796: don't let lines.marker affect the grid
Expand Down