bpo-46307: Add string.Template.get_identifiers() method (GH-30493)

Add `string.Template.get_identifiers()` method that returns the identifiers within the template. By default, raises an error if it encounters an invalid identifier (like `substitute()`). The keyword-only argument `raise_on_invalid` can be set to `False` to ignore invalid identifiers (like `safe_substitute()`).

Automerge-Triggered-By: GH:warsaw

1 files changed, 19 insertions, 0 deletions

diff --git a/Doc/library/string.rst b/Doc/library/string.rst
index b27782f..9bc703e 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -783,6 +783,22 @@ 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`.
+
+      .. versionadded:: 3.11
+
+
+   .. method:: get_identifiers()
+
+      Returns a list of the valid identifiers in the template, in the order
+      they first appear, ignoring any invalid identifiers.
+
+      .. versionadded:: 3.11
+
    :class:`Template` instances also provide one public data attribute:
 
    .. attribute:: template
@@ -869,6 +885,9 @@ rule:
 * *invalid* -- This group matches any other delimiter pattern (usually a single
   delimiter), and it should appear last in the regular expression.
 
+The methods on this class will raise :exc:`ValueError` if the pattern matches
+the template without one of these named groups matching.
+
 
 Helper functions
 ----------------