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Error with linestyles rcParams entries under the form (on, off, ...) and a style context manager #9792
Description
Bug summary
When defining an rcParams entry that is related to linestyle with an (on, off, ....) pattern, and using a style context manager somewhere in the code to temporarily apply other values of rcParams, an exception occurs.
Code for reproduction
Here is an example with the grid linestyle. (Related discussion on gitter.)
import matplotlib.pyplot as plt
from matplotlib import rcParams
rcParams["grid.linestyle"] = (4, 4) # no error with something liked "dotted"
fig = plt.figure()
with plt.style.context(["default"]):
ax0 = fig.add_subplot(121)
ax0.grid()
ax1 = fig.add_subplot(122)
ax1.grid()
#fig.savefig("test.png")Actual outcome
An exception is raised. With Matplotlib 2.1.0 and the master branch:
ValueError: Key grid.linestyle: linestyle (None, [4.0, 4.0]) is not a valid on-off ink sequence.
See at the end of the post for the full traceback.
I think this is occurs when exiting the style context manager. It looks like the linestyle given as (on, off, ...) is internally processed and stored into a form (offset, (on, off, ...)) that is actually not recognized by the line validator, which then raises an error when it is passed back to rcParams to restore the former style.
Please note that it may not even be due to the stricter linestyle validation that was introduced in Matplotlib 2.1 (#8040), as Matplotlib 2.0.2 as well as Matplotlib 1.5.3 also throw an exception, although slightly different:
ValueError: You passed in an invalid linestyle, `(4, 4)`. See docs of Line2D.set_linestyle for valid values.
Expected outcome
No exception when exiting the style context manager, and a plot with 2 different grid linestyles, both defined through the dedicated "grid.linestyle" entry in rcParams.
Matplotlib version
- Operating system: Linux (Fedora 26)
- Matplotlib version: 2.1.0 from conda, master, 1.5.3 and 2.0.2 from the git repo
- Matplotlib backend (
print(matplotlib.get_backend())): Qt5Agg - Python version: 3.6.3 from conda
Miscellaneous
The full traceback of the exception (with Matplotlib from the master branch):
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
~/FOSS/matplotlib/lib/matplotlib/rcsetup.py in _validate_linestyle(ls)
939
--> 940 return (None, validate_nseq_float()(ls))
941
~/FOSS/matplotlib/lib/matplotlib/rcsetup.py in __call__(self, s)
308 else val
--> 309 for val in s]
310 except ValueError:
~/FOSS/matplotlib/lib/matplotlib/rcsetup.py in <listcomp>(.0)
308 else val
--> 309 for val in s]
310 except ValueError:
TypeError: float() argument must be a string or a number, not 'NoneType'
During handling of the above exception, another exception occurred:
ValueError Traceback (most recent call last)
~/FOSS/matplotlib/lib/matplotlib/__init__.py in __setitem__(self, key, val)
911 try:
--> 912 cval = self.validate[key](val)
913 except ValueError as ve:
~/FOSS/matplotlib/lib/matplotlib/rcsetup.py in _validate_linestyle(ls)
945 raise ValueError("linestyle {!r} is not a valid on-off ink "
--> 946 "sequence.".format(ls))
947
ValueError: linestyle (None, [4.0, 4.0]) is not a valid on-off ink sequence.
During handling of the above exception, another exception occurred:
ValueError Traceback (most recent call last)
<ipython-input-7-3b8f6f6ce3da> in <module>()
8 with plt.style.context(["default"]):
9 ax0 = fig.add_subplot(121)
---> 10 ax0.grid()
11
12 ax1 = fig.add_subplot(122)
~/anaconda3/envs/matplotlib_dev/lib/python3.6/contextlib.py in __exit__(self, type, value, traceback)
86 if type is None:
87 try:
---> 88 next(self.gen)
89 except StopIteration:
90 return False
~/FOSS/matplotlib/lib/matplotlib/style/core.py in context(style, after_reset)
156 yield
157 finally:
--> 158 mpl.rcParams.update(initial_settings)
159
160
~/anaconda3/envs/matplotlib_dev/lib/python3.6/_collections_abc.py in update(*args, **kwds)
839 if isinstance(other, Mapping):
840 for key in other:
--> 841 self[key] = other[key]
842 elif hasattr(other, "keys"):
843 for key in other.keys():
~/FOSS/matplotlib/lib/matplotlib/__init__.py in __setitem__(self, key, val)
912 cval = self.validate[key](val)
913 except ValueError as ve:
--> 914 raise ValueError("Key %s: %s" % (key, str(ve)))
915 dict.__setitem__(self, key, cval)
916 except KeyError:
ValueError: Key grid.linestyle: linestyle (None, [4.0, 4.0]) is not a valid on-off ink sequence.
Activity
jklymak commentedon Nov 15, 2017
Any idea why these lines (
matplotlib/lib/matplotlib/__init__.py
Line 1326 in 3ccaf2d
dict.updateinstead of just copy or assign?tacaswell commentedon Nov 16, 2017
rcParamsis sometimes treated as a singleton so replacing it with a new dictionary may have surprising side effects. We are usingdict.updatehere to avoid re-validating things that we know are valid.I suspect that the linestyle validator needs to learn to understand the
(offset, [pattern])input.afvincent commentedon Nov 16, 2017
@tacaswell Yep, that is what I have in mind (adding the faulty input pattern to the validator).
afvincent commentedon Nov 16, 2017
With #9797, the exception is not raised anymore when running the above snippet.