Fix bug with space between operator and sub / superscripts.

Also add tests for it. A thin space should not be inserted in math text
between the operator and subscript / superscript.

Author: mpetroff

lib/matplotlib/mathtext.py

@@ -2894,10 +2894,10 @@ def operatorname(self, s, loc, toks):
                 hlist_list.append(c)
         next_char_loc = loc + len(toks[0]) + 1
         if isinstance(toks[0], ParseResults):
-            next_char_loc += 14  # Skip `operatorname{}`
+            next_char_loc += len('operatorname{}')
         next_char = next((c for c in s[next_char_loc:] if c != ' '), '')
         delimiters = self._left_delim | self._ambi_delim | self._right_delim
-        delimiters |= set(r"^_".split())
+        delimiters |= {'^', '_'}
         if (next_char not in delimiters and
                 toks[0] not in self._overunder_functions):
             # Add thin space except when followed by parenthesis, bracket, etc.

lib/matplotlib/tests/test_mathtext.py

@@ -297,12 +297,17 @@ def test_operator_space(fig_test, fig_ref):
     fig_test.text(0.1, 0.4, r"$\arcsin|6|$")
     fig_test.text(0.1, 0.5, r"$\operatorname{op} 6$")  # GitHub issue #553
     fig_test.text(0.1, 0.6, r"$\operatorname{op}[6]$")
+    fig_test.text(0.1, 0.7, r"$\cos^2$")
+    fig_test.text(0.1, 0.8, r"$\log_2$")
+
     fig_ref.text(0.1, 0.1, r"$\mathrm{log\,}6$")
     fig_ref.text(0.1, 0.2, r"$\mathrm{log}(6)$")
     fig_ref.text(0.1, 0.3, r"$\mathrm{arcsin\,}6$")
     fig_ref.text(0.1, 0.4, r"$\mathrm{arcsin}|6|$")
     fig_ref.text(0.1, 0.5, r"$\mathrm{op\,}6$")
     fig_ref.text(0.1, 0.6, r"$\mathrm{op}[6]$")
+    fig_ref.text(0.1, 0.7, r"$\mathrm{cos}^2$")
+    fig_ref.text(0.1, 0.8, r"$\mathrm{log}_2$")
 
 
 def test_mathtext_fallback_valid():