Fix #4855: Blacklist rcParams that aren't style

doc/users/whats_new/style_blacklist.rst

@@ -0,0 +1,11 @@
+Style parameter blacklist
+-------------------------
+
+In order to prevent unexpected consequences from using a style, style
+files are no longer able to set parameters that affect things
+unrelated to style.  These parameters include::
+
+  'interactive', 'backend', 'backend.qt4', 'webagg.port',
+  'webagg.port_retries', 'webagg.open_in_browser', 'backend_fallback',
+  'toolbar', 'timezone', 'datapath', 'figure.max_open_warning',
+  'savefig.directory', 'tk.window_focus', 'hardcopy.docstring'

lib/matplotlib/mpl-data/stylelib/classic.mplstyle

@@ -278,9 +278,6 @@ figure.facecolor : 0.75    # figure facecolor; 0.75 is scalar gray
 figure.edgecolor : w       # figure edgecolor
 figure.autolayout : False  # When True, automatically adjust subplot
                            # parameters to make the plot fit the figure
-figure.max_open_warning : 20  # The maximum number of figures to open through
-                              # the pyplot interface before emitting a warning.
-                              # If less than one this feature is disabled.
 figure.frameon : True
 
 # The figure subplot parameters.  All dimensions are a fraction of the
@@ -385,18 +382,13 @@ savefig.bbox        : standard # 'tight' or 'standard'.
                                # use ffmpeg_file instead
 savefig.pad_inches  : 0.1      # Padding to be used when bbox is set to 'tight'
 savefig.jpeg_quality: 95       # when a jpeg is saved, the default quality parameter.
-savefig.directory   : ~        # default directory in savefig dialog box,
-                               # leave empty to always use current working directory
 savefig.transparent : False    # setting that controls whether figures are saved with a
                                # transparent background by default
 savefig.frameon : True
 savefig.orientation : portrait
 
 nbagg.transparent: True
 
-# tk backend params
-tk.window_focus   : False    # Maintain shell focus for TkAgg
-
 # ps backend params
 ps.papersize      : letter   # auto, letter, legal, ledger, A0-A10, B0-B10
 ps.useafm         : False    # use of afm fonts, results in small files
@@ -418,7 +410,7 @@ pdf.use14corefonts : False
 pgf.debug           : False
 pgf.texsystem       : xelatex
 pgf.rcfonts         : True
-pgf.preamble        : 
+pgf.preamble        :
 
 # svg backend params
 svg.image_inline : True       # write raster image data directly into the svg file
@@ -467,8 +459,6 @@ keymap.yscale : l                   # toggle scaling of y-axes ('log'/'linear')
 keymap.xscale : k, L                # toggle scaling of x-axes ('log'/'linear')
 keymap.all_axes : a                 # enable all axes
 
-toolbar: toolbar2
-
 ###ANIMATION settings
 animation.writer : ffmpeg         # MovieWriter 'backend' to use
 animation.codec : mpeg4           # Codec to use for writing movie

lib/matplotlib/style/core.py

@@ -18,10 +18,11 @@
 import os
 import re
 import contextlib
+import warnings
 
 import matplotlib as mpl
 from matplotlib import cbook
-from matplotlib import rc_params_from_file
+from matplotlib import rc_params_from_file, rcParamsDefault
 
 
 __all__ = ['use', 'context', 'available', 'library', 'reload_library']
@@ -34,11 +35,35 @@
 STYLE_FILE_PATTERN = re.compile('([\S]+).%s$' % STYLE_EXTENSION)
 
 
+# A list of rcParams that should not be applied from styles
+STYLE_BLACKLIST = set([
+    'interactive', 'backend', 'backend.qt4', 'webagg.port',
+    'webagg.port_retries', 'webagg.open_in_browser', 'backend_fallback',
+    'toolbar', 'timezone', 'datapath', 'figure.max_open_warning',
+    'savefig.directory', 'tk.window_focus', 'hardcopy.docstring'])
+
+
+def _remove_blacklisted_style_params(d):
+    o = {}
+    for key, val in d.items():
+        if key in STYLE_BLACKLIST:
+            warnings.warn(
+                "Style includes a parameter, '{0}', that is not related to "
+                "style.  Ignoring".format(key))
+        else:
+            o[key] = val
+    return o
+
+
 def is_style_file(filename):
     """Return True if the filename looks like a style file."""
     return STYLE_FILE_PATTERN.match(filename) is not None
 
 
+def _apply_style(d):
+    mpl.rcParams.update(_remove_blacklisted_style_params(d))
+
+
 def use(style):
     """Use matplotlib style settings from a style specification.
 
@@ -71,18 +96,15 @@ def use(style):
 
     for style in styles:
         if not cbook.is_string_like(style):
-            mpl.rcParams.update(style)
-            continue
+            _apply_style(style)
         elif style == 'default':
-            mpl.rcdefaults()
-            continue
-
-        if style in library:
-            mpl.rcParams.update(library[style])
+            _apply_style(rcParamsDefault)
+        elif style in library:
+            _apply_style(library[style])
         else:
             try:
                 rc = rc_params_from_file(style, use_default_template=False)
-                mpl.rcParams.update(rc)
+                _apply_style(rc)
             except IOError:
                 msg = ("'%s' not found in the style library and input is "
                        "not a valid URL or path. See `style.available` for "