plotting (with custom PNG viewer as per trac 11795) can silently fail

[greg-minshall]

hi. with #11795 installed, misconfiguring the, e.g., PNG viewer causes a plot to fail silently.

import sage.misc.viewer
viewer.png_viewer('/x/y/display')
circle((0,0), 1, rgbcolor=(1,1,0))

note the "e.g." above. the same thing happens for PDF and DVI files. browser, on the other hand, reports an error:

sage: viewer.browser('/x/y/w3m')
sage: tutorial()
/Users/buildsage/src/import/sage/sage-5.4.1/local/bin/sage-native-execute: line 8: /x/y/w3m: No such file or directory

on the mailing list, Ivan Andrus commented thus:

That's true. The function specifically sends all output to /dev/null, so there's probably some reason for doing that. But we could at least use the exit status to print a warning that it might not work.

(ps -- let me know about formatting, tagging, etc., mistakes i may have made.)

CC: @nathanncohen @gvol

Component: user interface

Issue created by migration from https://trac.sagemath.org/ticket/13842

[ppurka]

comment:2

The file sage/misc/viewer.py passes all the doctests precisely because it does not care whether the commands that are being doctested are actually present in the system. I tried adding a check and then almost everything fails.

How should I go about adding the test for a command then? Introduce a new keyword to the Viewer._set() method called check_command=True?

[jhpalmieri]

comment:3

To add a test use sage.doctest.DOCTEST_MODE in the code to avoid user settings, as in for example sage/misc/hg.py or sage/plot/animate.py.