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Description
In my investigation of image comparison fails with pytest and xdist plugin I have discovered strange behavior. By changing the extensions order of the image comparison tests you will receive different output (and of course test failures).
I made extensions shufflelike this and gotthese results. From the log you can see that mostly affected are legend tests on svg backend. So any baseline image from the tests withlegend call is spoiled by pdf backend, except thelegend +tightbox.
I tried to compare figure state before and aftersavefig call but run into issue#6870.
Here is the way to reproduce the problem. You can compare output of the snippet with baseline images ofmatplotlib.tests.test_legend.test_legend_auto1 test, if you want.
# python savefig_sideeffects.py svg svg pdf svg# diff -u 0.svg 1.svg# diff -u 1.svg 3.svg# SOURCE_DATE_EPOCH=0 python savefig_sideeffects.py pdf pdf svg pdfimportnumpyasnpimportmatplotlibmatplotlib.use('agg')importmatplotlib.pylabasplt# matplotlib.testing.decorators.ImageComparisonTest.remove_textdefremove_text(figure):frommatplotlibimporttickerfigure.suptitle("")foraxinfigure.get_axes():ax.set_title("")ax.xaxis.set_major_formatter(ticker.NullFormatter())ax.xaxis.set_minor_formatter(ticker.NullFormatter())ax.yaxis.set_major_formatter(ticker.NullFormatter())ax.yaxis.set_minor_formatter(ticker.NullFormatter())try:ax.zaxis.set_major_formatter(ticker.NullFormatter())ax.zaxis.set_minor_formatter(ticker.NullFormatter())exceptAttributeError:pass# matplotlib.tests.test_legend.test_legend_auto1deftest_legend_auto1():'Test automatic legend placement'fig=plt.figure()ax=fig.add_subplot(111)x=np.arange(100)ax.plot(x,50-x,'o',label='y=1')ax.plot(x,x-50,'o',label='y=-1')ax.legend(loc=0)returnfigdefprepare():importmatplotlib.testingmatplotlib._init_tests()# matplotlib.testing.decorators.ImageComparisonTest.setup_classmatplotlib.testing.setup()matplotlib.style.use('classic')matplotlib.testing.set_font_settings_for_testing()fig=test_legend_auto1()remove_text(fig)returnfigdeftest(exts):fig=prepare()# this will stick svg path ids with the same valuesmatplotlib.rc('svg',hashsalt='asdf')forpinenumerate(exts):fig.savefig('%d.%s'%p)if__name__=='__main__':importsystest(sys.argv[1:])
This is the demonstration of the issue, wheresavefig with pdf backend has sideeffect on the nextsavefig with svg backend:
>python savefig_sideeffects.py svg svg pdf svg>diff -u 0.svg 1.svg>diff -u 1.svg 3.svg--- 1.svg 2016-08-04 00:29:52.429050200 +0300+++ 3.svg 2016-08-04 00:29:52.537061000 +0300@@ -462,18 +462,18 @@ </g> <g> <g>- <path d="M 424.413 239.2965-L 511.2 239.2965-L 511.2 192.7035-L 424.413 192.7035+ <path d="M 424.469375 239.25225+L 511.2 239.25225+L 511.2 192.74775+L 424.469375 192.74775 z "/> </g> <g/> <g> <g>- <use x="434.493" xlink:href="#mb9df33688a" y="204.36525"/>- <use x="454.653" xlink:href="#mb9df33688a" y="204.36525"/>+ <use x="434.549375" xlink:href="#mb9df33688a" y="204.4095"/>+ <use x="454.709375" xlink:href="#mb9df33688a" y="204.4095"/> </g> </g> <g>@@ -520,7 +520,7 @@ z "/> </defs>- <g transform="translate(470.493 209.40525)scale(0.144 -0.144)">+ <g transform="translate(470.549375 209.4495)scale(0.144 -0.144)"> <use xlink:href="#DejaVuSans-79"/> <use x="59.179688" xlink:href="#DejaVuSans-3d"/> <use x="142.96875" xlink:href="#DejaVuSans-31"/>@@ -529,8 +529,8 @@ <g/> <g> <g>- <use x="434.493" xlink:href="#m3d71661f95" y="225.50175"/>- <use x="454.653" xlink:href="#m3d71661f95" y="225.50175"/>+ <use x="434.549375" xlink:href="#m3d71661f95" y="225.546"/>+ <use x="454.709375" xlink:href="#m3d71661f95" y="225.546"/> </g> </g> <g>@@ -543,7 +543,7 @@ z "/> </defs>- <g transform="translate(470.493 230.54175)scale(0.144 -0.144)">+ <g transform="translate(470.549375 230.586)scale(0.144 -0.144)"> <use xlink:href="#DejaVuSans-79"/> <use x="59.179688" xlink:href="#DejaVuSans-3d"/> <use x="142.96875" xlink:href="#DejaVuSans-2d"/>
Same happens to pdf after svg.
By accident, while fixing issue#6870, it seems that I have fixed this too. Test above now passes but there are 505 SVG baseline images affected and need update. I will open PR for this soon.