BUG: allow unicode column_format in to_latex

this is an internal method, and the kwd args is not used anywhere,
still...

Author: y-p

pandas/core/format.py

@@ -298,7 +298,7 @@ def to_latex(self, force_unicode=False, column_format=None):
         if column_format is None:
             column_format = '|l|%s|' % '|'.join('c' for _ in strcols)
         else:
-            assert isinstance(column_format, str)
+            assert isinstance(column_format, basestring)
 
         self.buf.write('\\begin{tabular}{%s}\n' % column_format)
         self.buf.write('\\hline\n')