Use cbook string class checker

dstansby · dstansby · commit abcef5afd54e · 2016-12-22T12:07:32.000Z
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -1282,7 +1282,7 @@ def set_aspect(self, aspect, adjustable=None, anchor=None):
           etc.
           =====   =====================
         """
-        if isinstance(aspect, str) and aspect in ('equal', 'auto'):
+        if cbook.is_string_like(aspect) and aspect in ('equal', 'auto'):
             self._aspect = aspect
         else:
             self._aspect = float(aspect)  # raise ValueError if necessary
