matplotlib
diff --git a/‎doc/api/next_api_changes/deprecations.rst
Lines changed: 6 additions & 0 deletions b/‎doc/api/next_api_changes/deprecations.rst
Lines changed: 6 additions & 0 deletions
diff --git a/‎lib/matplotlib/rcsetup.py
Lines changed: 17 additions & 7 deletions b/‎lib/matplotlib/rcsetup.py
Lines changed: 17 additions & 7 deletions
diff --git a/‎lib/matplotlib/tests/test_backend_pgf.py
Lines changed: 5 additions & 5 deletions b/‎lib/matplotlib/tests/test_backend_pgf.py
Lines changed: 5 additions & 5 deletions
diff --git a/‎lib/matplotlib/tests/test_cycles.py
Lines changed: 1 addition & 1 deletion b/‎lib/matplotlib/tests/test_cycles.py
Lines changed: 1 addition & 1 deletion
diff --git a/‎lib/matplotlib/tests/test_rcparams.py
Lines changed: 1 addition & 1 deletion b/‎lib/matplotlib/tests/test_rcparams.py
Lines changed: 1 addition & 1 deletion
diff --git a/‎lib/matplotlib/tests/test_texmanager.py
Lines changed: 1 addition & 1 deletion b/‎lib/matplotlib/tests/test_texmanager.py
Lines changed: 1 addition & 1 deletion
@@ -59,3 +59,9 @@ Passing raw data via parameters *data* and *lut* to `.register_cmap()` is
 deprecated. Instead, explicitly create a `.LinearSegmentedColormap` and pass
 it via the *cmap* parameter:
 ``register_cmap(cmap=LinearSegmentedColormap(name, data, lut))``.
+
+Setting :rc:`text.latex.preamble` or :rc:`pdf.preamble` to non-strings
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+These rcParams should be set to string values.  Support for None (meaning the
+empty string) and lists of strings (implicitly joined with newlines) is
+deprecated.
@@ -15,7 +15,6 @@
 """
 
 import ast
-from collections.abc import Iterable, Mapping
 from functools import partial, reduce
 import logging
 from numbers import Number
@@ -86,11 +85,9 @@ def f(s):
                             for v in s if v.strip()]
                 else:
                     raise
-        # We should allow any generic sequence type, including generators,
-        # Numpy ndarrays, and pandas data structures.  However, unordered
-        # sequences, such as sets, should be allowed but discouraged unless the
-        # user desires pseudorandom behavior.
-        elif isinstance(s, Iterable) and not isinstance(s, Mapping):
+        # Allow any ordered sequence type -- generators, np.ndarray, pd.Series
+        # -- but not sets, whose iteration order is non-deterministic.
+        elif np.iterable(s) and not isinstance(s, (set, frozenset)):
             # The condition on this list comprehension will preserve the
             # behavior of filtering out any empty strings (behavior was
             # from the original validate_stringlist()), while allowing
@@ -104,6 +101,7 @@ def f(s):
         f.__name__ = "{}list".format(scalar_validator.__name__)
     except AttributeError:  # class instance.
         f.__name__ = "{}List".format(type(scalar_validator).__name__)
+    f.__qualname__ = f.__qualname__.rsplit(".", 1)[0] + "." + f.__name__
     f.__doc__ = doc if doc is not None else scalar_validator.__doc__
     return f
 
@@ -151,12 +149,19 @@ def validate_bool_maybe_none(b):
 
 
 def _validate_tex_preamble(s):
+    message = (
+        f"Support for setting the 'text.latex.unicode' and 'pdf.preamble' "
+        f"rcParams to {s!r} is deprecated since %(since)s and will be "
+        f"removed %(removal)s; please set them to plain (possibly empty) "
+        f"strings instead.")
     if s is None or s == 'None':
+        cbook.warn_deprecated("3.3", message=message)
         return ""
     try:
         if isinstance(s, str):
             return s
-        elif isinstance(s, Iterable):
+        elif np.iterable(s):
+            cbook.warn_deprecated("3.3", message=message)
             return '\n'.join(s)
         else:
             raise TypeError
@@ -202,6 +207,11 @@ def validator(s):
         except ValueError:
             raise ValueError(f'Could not convert {s!r} to {cls.__name__}')
 
+    validator.__name__ = f"validate_{cls.__name__}"
+    if allow_none:
+        validator.__name__ += "_or_None"
+    validator.__qualname__ = (
+        validator.__qualname__.rsplit(".", 1)[0] + "." + validator.__name__)
     return validator
 
 
 
@@ -111,8 +111,8 @@ def test_pdflatex():
     rc_pdflatex = {'font.family': 'serif',
                    'pgf.rcfonts': False,
                    'pgf.texsystem': 'pdflatex',
-                   'pgf.preamble': ['\\usepackage[utf8x]{inputenc}',
-                                    '\\usepackage[T1]{fontenc}']}
+                   'pgf.preamble': ('\\usepackage[utf8x]{inputenc}'
+                                    '\\usepackage[T1]{fontenc}')}
     mpl.rcParams.update(rc_pdflatex)
     create_figure()
 
@@ -136,9 +136,9 @@ def test_rcupdate():
                 'lines.markersize': 20,
                 'pgf.rcfonts': False,
                 'pgf.texsystem': 'pdflatex',
-                'pgf.preamble': ['\\usepackage[utf8x]{inputenc}',
-                                 '\\usepackage[T1]{fontenc}',
-                                 '\\usepackage{sfmath}']}]
+                'pgf.preamble': ('\\usepackage[utf8x]{inputenc}'
+                                 '\\usepackage[T1]{fontenc}'
+                                 '\\usepackage{sfmath}')}]
     tol = [6, 0]
     for i, rc_set in enumerate(rc_sets):
         with mpl.rc_context(rc_set):
 
@@ -184,7 +184,7 @@ def test_invalid_input_forms():
     with pytest.raises((TypeError, ValueError)):
         ax.set_prop_cycle('linewidth', 1)
     with pytest.raises((TypeError, ValueError)):
-        ax.set_prop_cycle('linewidth', {'1': 1, '2': 2})
+        ax.set_prop_cycle('linewidth', {1, 2})
     with pytest.raises((TypeError, ValueError)):
         ax.set_prop_cycle(linewidth=1, color='r')
 
 
@@ -218,7 +218,7 @@ def generate_validator_testcases(valid):
                      ((1, 2), ['1', '2']),
                      (np.array([1, 2]), ['1', '2']),
                      ),
-         'fail': ((dict(), ValueError),
+         'fail': ((set(), ValueError),
                   (1, ValueError),
                   )
          },
 
@@ -11,7 +11,7 @@ def test_fontconfig_preamble():
     tm1 = TexManager()
     font_config1 = tm1.get_font_config()
 
-    plt.rcParams['text.latex.preamble'] = ['\\usepackage{txfonts}']
+    plt.rcParams['text.latex.preamble'] = '\\usepackage{txfonts}'
     tm2 = TexManager()
     font_config2 = tm2.get_font_config()