Barry Warsaw  committed 5afa527

SF patch #1056967, changes the semantics of Template.safe_substitute() to not
raise a ValueError for dangling delimiters (the delimiter itself is returned).

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  • Parent commits 80ca1a8
  • Branches legacy-trunk

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File Doc/lib/libstring.tex

 Like \method{substitute()}, except that if placeholders are missing from
 \var{mapping} and \var{kws}, instead of raising a \exception{KeyError}
 exception, the original placeholder will appear in the resulting string
-intact.  Note that other exceptions may still be raised, including
-\exception{ValueError} as described above.
+intact.  Also, unlike with \method{substitute()}, any other appearances of the
+\samp{\$} will simply return \samp{\$} instead of raising
+While other exceptions may still occur, this method is called ``safe'' because
+substitutions always tries to return a usable string instead of raising an
+exception.  In another sense, \method{safe_substitute()} may be anything other
+than safe, since it will silently ignore malformed templates containing
+dangling delimiters, unmatched braces, or placeholders that are not valid
+Python identifiers.
 \class{Template} instances also provide one public data attribute:

File Lib/

             if'escaped') is not None:
                 return self.delimiter
             if'invalid') is not None:
-                self._invalid(mo)
+                return self.delimiter
             raise ValueError('Unrecognized named group in pattern',
         return self.pattern.sub(convert, self.template)

File Lib/test/

         raises(TypeError, s.safe_substitute, d, {})
     def test_delimiter_override(self):
+        eq = self.assertEqual
+        raises = self.assertRaises
         class AmpersandTemplate(Template):
             delimiter = '&'
         s = AmpersandTemplate('this &gift is for &{who} &&')
-        self.assertEqual(s.substitute(gift='bud', who='you'),
-                         'this bud is for you &')
-        self.assertRaises(KeyError, s.substitute)
-        self.assertEqual(s.safe_substitute(gift='bud', who='you'),
-                         'this bud is for you &')
-        self.assertEqual(s.safe_substitute(),
-                         'this &gift is for &{who} &')
+        eq(s.substitute(gift='bud', who='you'), 'this bud is for you &')
+        raises(KeyError, s.substitute)
+        eq(s.safe_substitute(gift='bud', who='you'), 'this bud is for you &')
+        eq(s.safe_substitute(), 'this &gift is for &{who} &')
         s = AmpersandTemplate('this &gift is for &{who} &')
-        self.assertRaises(ValueError, s.substitute,
-                          dict(gift='bud', who='you'))
-        self.assertRaises(ValueError, s.safe_substitute)
+        raises(ValueError, s.substitute, dict(gift='bud', who='you'))
+        eq(s.safe_substitute(), 'this &gift is for &{who} &')
 def test_main():
     from test import test_support
+- Patch #1056967 changes the semantics of Template.safe_substitute() so that
+  no ValueError is raised on an 'invalid' match group.  Now the delimiter is
+  returned.
 - Bug #1052503 pdb.runcall() was not passing along keyword arguments.
 - Bug #902037: XML.sax.saxutils.prepare_input_source() now combines relative