further fixes

Author: fchapoton

src/sage/typeset/ascii_art.py

@@ -181,7 +181,6 @@ class AsciiArt(CharacterArt):
          pi*x
         e
     """
-    _string_type = str
 
 
 _ascii_art_factory = CharacterArtFactory(

src/sage/typeset/character_art.py

@@ -103,8 +103,7 @@ def empty(cls):
             sage: from sage.typeset.ascii_art import AsciiArt
             sage: AsciiArt.empty()
         """
-        empty_string = cls._string_type()
-        return cls([empty_string])
+        return cls([''])
 
     def __getitem__(self, key):
         r"""
@@ -167,7 +166,7 @@ def __format__(self, fmt):
             sage: format(unicode_art(M))                                                # needs sage.modules
             '\u239b1 2\u239e\n\u239d3 4\u23a0'
         """
-        return format(self._string_type(self), fmt)
+        return format(str(self), fmt)
 
     def get_baseline(self):
         r"""

src/sage/typeset/unicode_art.py

@@ -49,7 +49,6 @@ class UnicodeArt(CharacterArt):
          π⋅x
         ℯ
     """
-    _string_type = str
 
 
 _unicode_art_factory = CharacterArtFactory(