diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
index 2b0833f215c9..4add79be995b 100644
--- a/lib/matplotlib/rcsetup.py
+++ b/lib/matplotlib/rcsetup.py
@@ -25,7 +25,7 @@
import warnings
import re
-from matplotlib.cbook import mplDeprecation, deprecated, ls_mapper
+from matplotlib.cbook import mplDeprecation, deprecated, ls_mapper, iterable
from matplotlib.fontconfig_pattern import parse_fontconfig_pattern
from matplotlib.colors import is_color_like
@@ -931,13 +931,29 @@ def _validate_linestyle(ls):
"sequence nor a valid string.".format(ls))
# Look for an on-off ink sequence (in points) *of even length*.
- # Offset is set to None.
+ # Offset is set to None if not present.
try:
+ offset = None
+ # Look first for the case (offset, on-off seq). Take also care of the
+ # historically supported corner-case of an on-off seq like ["1", "2"].
+ if (len(ls) == 2 and iterable(ls[1]) and
+ not isinstance(ls[0], six.string_types)):
+ # That is likely to be a pattern (offset, on-off seq), so extract
+ # the offset and continue with the on-off sequence candidate.
+ if ls[0] is not None:
+ try:
+ offset = float(ls[0])
+ except ValueError:
+ raise ValueError(
+ "a linestyle offset should be None or "
+ "a numerical value, not {!r}.".format(ls[0]))
+ offset, ls = ls
+
if len(ls) % 2 != 0:
raise ValueError("the linestyle sequence {!r} is not of even "
"length.".format(ls))
- return (None, validate_nseq_float()(ls))
+ return (offset, validate_nseq_float()(ls))
except (ValueError, TypeError):
# TypeError can be raised inside the instance of validate_nseq_float,
diff --git a/lib/matplotlib/tests/test_rcparams.py b/lib/matplotlib/tests/test_rcparams.py
index 06650de2b37b..71b8dc48d9a2 100644
--- a/lib/matplotlib/tests/test_rcparams.py
+++ b/lib/matplotlib/tests/test_rcparams.py
@@ -375,14 +375,18 @@ def generate_validator_testcases(valid):
(['1.23', '4.56'], (None, [1.23, 4.56])),
([1.23, 456], (None, [1.23, 456.0])),
([1, 2, 3, 4], (None, [1.0, 2.0, 3.0, 4.0])),
+ ((-1, [1.23, 456]), (-1, [1.23, 456.0])),
+ ((None, [1.23, 456]), (None, [1.23, 456.0])),
+ ((9.87, [1.23, 456]), (9.87, [1.23, 456.0])),
+ ((np.float128(1), [1.23, 4]), (1.0, [1.23, 4.0])),
),
'fail': (('aardvark', ValueError), # not a valid string
('dotted'.encode('utf-16'), ValueError), # even on PY2
- ((None, [1, 2]), ValueError), # (offset, dashes) != OK
- ((0, [1, 2]), ValueError), # idem
- ((-1, [1, 2]), ValueError), # idem
([1, 2, 3], ValueError), # sequence with odd length
(1.23, ValueError), # not a sequence
+ (("a", [1, 2]), ValueError), # wrong explicit offset
+ ((1, [1, 2, 3]), ValueError), # odd length sequence
+ (([1, 2], 1), ValueError), # inverted offset/onoff
)
}
# Add some cases of bytes arguments that Python 2 can convert silently:
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