Simplify validate_color, and make it slightly stricter.

anntzer · anntzer · commit a0ff63149a96 · 2020-02-13T01:41:23.000+01:00
Previously, validate_color would accept nonsensical strings such as
`".a2,.2f4,.6"` by dropping the letters and just reading the rest (i.e.
`(0.2, 0.24, 0.6)`.  Reject such inputs now, and make the parsing much
simpler (it's just ast.literal_eval).

The only vaguely reasonable string that was accepted and that is not
accepted anymore is (e.g.) `'(0, 1, "0.5")'` (the quotes would be
dropped), i.e. one could write `rcParams["lines.color"] = '(0, 1, "0.5")'`.
I think this can also be dropped given that the corresponding
`rcParams["lines.color"] = (0, 1, "0.5")` (passing in the tuple
directly) didn't work...

I added a changelog entry just to be safe, but it's the kind of entry
that's probably just going to confuse everyone with no real benefit...
diff --git a/doc/api/next_api_changes/behaviour.rst b/doc/api/next_api_changes/behaviour.rst
@@ -78,3 +78,10 @@ instead.
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 This creates the stem plot as a `.LineCollection` rather than individual
 `.Line2D` objects, greatly improving performance.
+
+rcParams color validator is now stricter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Previously, rcParams entries whose values were color-like accepted "spurious"
+extra letters or characters in the "middle" of the string, e.g. ``"(0, 1a, '0.5')"``
+would be interpreted as ``(0, 1, 0.5)``.  These extra characters (including the
+internal quotes) now cause a ValueError to be raised.
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -326,13 +326,9 @@ def validate_color_for_prop_cycle(s):
 
 def validate_color(s):
     """Return a valid color arg."""
-    try:
+    if isinstance(s, str):
         if s.lower() == 'none':
             return 'none'
-    except AttributeError:
-        pass
-
-    if isinstance(s, str):
         if len(s) == 6 or len(s) == 8:
             stmp = '#' + s
             if is_color_like(stmp):
@@ -341,25 +337,16 @@ def validate_color(s):
     if is_color_like(s):
         return s
 
-    # If it is still valid, it must be a tuple.
-    colorarg = s
-    msg = ''
-    if s.find(',') >= 0:
-        # get rid of grouping symbols
-        stmp = ''.join([c for c in s if c.isdigit() or c == '.' or c == ','])
-        vals = stmp.split(',')
-        if len(vals) not in [3, 4]:
-            msg = '\nColor tuples must be of length 3 or 4'
-        else:
-            try:
-                colorarg = [float(val) for val in vals]
-            except ValueError:
-                msg = '\nCould not convert all entries to floats'
-
-    if not msg and is_color_like(colorarg):
-        return colorarg
+    # If it is still valid, it must be a tuple (as a string from matplotlibrc).
+    try:
+        color = ast.literal_eval(s)
+    except (SyntaxError, ValueError):
+        pass
+    else:
+        if is_color_like(color):
+            return color
 
-    raise ValueError('%s does not look like a color arg%s' % (s, msg))
+    raise ValueError(f'{s!r} does not look like a color arg')
 
 
 validate_colorlist = _listify_validator(
diff --git a/lib/matplotlib/tests/test_rcparams.py b/lib/matplotlib/tests/test_rcparams.py
@@ -310,16 +310,16 @@ def generate_validator_testcases(valid):
                      ('AABBCC00', '#AABBCC00'),  # RGBA hex code
                      ('tab:blue', 'tab:blue'),  # named color
                      ('C12', 'C12'),  # color from cycle
-                     ('(0, 1, 0)', [0.0, 1.0, 0.0]),  # RGB tuple
+                     ('(0, 1, 0)', (0.0, 1.0, 0.0)),  # RGB tuple
                      ((0, 1, 0), (0, 1, 0)),  # non-string version
-                     ('(0, 1, 0, 1)', [0.0, 1.0, 0.0, 1.0]),  # RGBA tuple
+                     ('(0, 1, 0, 1)', (0.0, 1.0, 0.0, 1.0)),  # RGBA tuple
                      ((0, 1, 0, 1), (0, 1, 0, 1)),  # non-string version
-                     ('(0, 1, "0.5")', [0.0, 1.0, 0.5]),  # unusual but valid
                      ),
          'fail': (('tab:veryblue', ValueError),  # invalid name
                   ('(0, 1)', ValueError),  # tuple with length < 3
                   ('(0, 1, 0, 1, 0)', ValueError),  # tuple with length > 4
                   ('(0, 1, none)', ValueError),  # cannot cast none to float
+                  ('(0, 1, "0.5")', ValueError),  # last one not a float
                   ),
          },
         {'validator': validate_hist_bins,
