bpo-46307: Add string.Template.is_valid method

benkehoe · benkehoe · commit e80bb26926ec · 2022-01-10T19:03:43.000-07:00
diff --git a/Doc/library/string.rst b/Doc/library/string.rst
@@ -783,6 +783,18 @@ these rules.  The methods of :class:`Template` are:
       templates containing dangling delimiters, unmatched braces, or
       placeholders that are not valid Python identifiers.
 
+
+   .. method:: is_valid()
+
+      Returns false if the template has invalid placeholders that will cause
+      :meth:`substitute` to raise :exc:`ValueError`.
+
+
+   .. method:: get_identifiers()
+
+      Returns a list of the valid identifiers in the template, in the order
+      they first appear, ignoring any invalid identifiers.
+
    :class:`Template` instances also provide one public data attribute:
 
    .. attribute:: template
diff --git a/Lib/string.py b/Lib/string.py
@@ -141,14 +141,33 @@ def convert(mo):
                              self.pattern)
         return self.pattern.sub(convert, self.template)
 
-    def get_identifiers(self, *, raise_on_invalid=True):
+    def is_valid(self):
+        for mo in self.pattern.finditer(self.template):
+            if mo.group('invalid') is not None:
+                return False
+            if (mo.group('named') is None
+                and mo.group('braced') is None
+                and mo.group('escaped') is None):
+                # If all the groups are None, there must be
+                # another group we're not expecting
+                raise ValueError('Unrecognized named group in pattern',
+                    self.pattern)
+        return True
+
+    def get_identifiers(self):
         ids = []
         for mo in self.pattern.finditer(self.template):
             named = mo.group('named') or mo.group('braced')
             if named is not None and named not in ids:
+                # add a named group only the first time it appears
                 ids.append(named)
-            elif mo.group('invalid') is not None and raise_on_invalid:
-                self._invalid(mo)
+            elif (named is None
+                and mo.group('invalid') is None
+                and mo.group('escaped') is None):
+                # If all the groups are None, there must be
+                # another group we're not expecting
+                raise ValueError('Unrecognized named group in pattern',
+                    self.pattern)
         return ids
 
 # Initialize Template.pattern.  __init_subclass__() is automatically called
diff --git a/Lib/test/test_string.py b/Lib/test/test_string.py
@@ -475,6 +475,27 @@ class PieDelims(Template):
         self.assertEqual(s.substitute(dict(who='tim', what='ham')),
                          'tim likes to eat a bag of ham worth $100')
 
+    def test_is_valid(self):
+        eq = self.assertEqual
+        s = Template('$who likes to eat a bag of ${what} worth $$100')
+        self.assertTrue(s.is_valid())
+
+        s = Template('$who likes to eat a bag of ${what} worth $100')
+        self.assertFalse(s.is_valid())
+
+        # if the pattern has an unrecognized capture group,
+        # it should raise ValueError like substitute and safe_substitute do
+        class BadPattern(Template):
+            pattern = r"""
+            (?P<badname>.*)                  |
+            (?P<escaped>@{2})                   |
+            @(?P<named>[_a-z][._a-z0-9]*)       |
+            @{(?P<braced>[_a-z][._a-z0-9]*)}    |
+            (?P<invalid>@)                      |
+            """
+        s = BadPattern('@bag.foo.who likes to eat a bag of @bag.what')
+        self.assertRaises(ValueError, s.is_valid)
+
     def test_get_identifiers(self):
         eq = self.assertEqual
         raises = self.assertRaises
@@ -487,15 +508,24 @@ def test_get_identifiers(self):
         ids = s.get_identifiers()
         eq(ids, ['who', 'what'])
 
-        # invalid identifiers are raised
-        s = Template('$who likes to eat a bag of ${what} worth $100')
-        raises(ValueError, s.get_identifiers)
-
-        # invalid identifiers are ignored with raise_on_invalid=False
+        # invalid identifiers are ignored
         s = Template('$who likes to eat a bag of ${what} worth $100')
-        ids = s.get_identifiers(raise_on_invalid=False)
+        ids = s.get_identifiers()
         eq(ids, ['who', 'what'])
 
+        # if the pattern has an unrecognized capture group,
+        # it should raise ValueError like substitute and safe_substitute do
+        class BadPattern(Template):
+            pattern = r"""
+            (?P<badname>.*)                  |
+            (?P<escaped>@{2})                   |
+            @(?P<named>[_a-z][._a-z0-9]*)       |
+            @{(?P<braced>[_a-z][._a-z0-9]*)}    |
+            (?P<invalid>@)                      |
+            """
+        s = BadPattern('@bag.foo.who likes to eat a bag of @bag.what')
+        self.assertRaises(ValueError, s.get_identifiers)
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2022-01-10-07-51-43.bpo-46307.SKvOIY.rst b/Misc/NEWS.d/next/Library/2022-01-10-07-51-43.bpo-46307.SKvOIY.rst
@@ -1 +1 @@
-Add :meth:`string.Template.get_identifiers` method.
+Add :meth:`string.Template.is_valid` and :meth:`string.Template.get_identifiers` methods.

Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		-Add :meth:`string.Template.get_identifiers` method.
	`1`	+Add :meth:`string.Template.is_valid` and :meth:`string.Template.get_identifiers` methods.