Upgrade string from CPython 3.14.2

Lib/string/__init__.py

@@ -49,11 +49,18 @@ def capwords(s, sep=None):
 
 
 ####################################################################
-import re as _re
-from collections import ChainMap as _ChainMap
-
 _sentinel_dict = {}
 
+
+class _TemplatePattern:
+    # This descriptor is overwritten in ``Template._compile_pattern()``.
+    def __get__(self, instance, cls=None):
+        if cls is None:
+            return self
+        return cls._compile_pattern()
+_TemplatePattern = _TemplatePattern()
+
+
 class Template:
     """A string class for supporting $-substitutions."""
 
@@ -64,14 +71,21 @@ class Template:
     # See https://bugs.python.org/issue31672
     idpattern = r'(?a:[_a-z][_a-z0-9]*)'
     braceidpattern = None
-    flags = _re.IGNORECASE
+    flags = None  # default: re.IGNORECASE
+
+    pattern = _TemplatePattern  # use a descriptor to compile the pattern
 
     def __init_subclass__(cls):
         super().__init_subclass__()
-        if 'pattern' in cls.__dict__:
-            pattern = cls.pattern
-        else:
-            delim = _re.escape(cls.delimiter)
+        cls._compile_pattern()
+
+    @classmethod
+    def _compile_pattern(cls):
+        import re  # deferred import, for performance
+
+        pattern = cls.__dict__.get('pattern', _TemplatePattern)
+        if pattern is _TemplatePattern:
+            delim = re.escape(cls.delimiter)
             id = cls.idpattern
             bid = cls.braceidpattern or cls.idpattern
             pattern = fr"""
@@ -82,7 +96,10 @@ class Template:
               (?P<invalid>)             # Other ill-formed delimiter exprs
             )
             """
-        cls.pattern = _re.compile(pattern, cls.flags | _re.VERBOSE)
+        if cls.flags is None:
+            cls.flags = re.IGNORECASE
+        pat = cls.pattern = re.compile(pattern, cls.flags | re.VERBOSE)
+        return pat
 
     def __init__(self, template):
         self.template = template
@@ -105,7 +122,8 @@ class Template:
         if mapping is _sentinel_dict:
             mapping = kws
         elif kws:
-            mapping = _ChainMap(kws, mapping)
+            from collections import ChainMap
+            mapping = ChainMap(kws, mapping)
         # Helper function for .sub()
         def convert(mo):
             # Check the most common path first.
@@ -124,7 +142,8 @@ class Template:
         if mapping is _sentinel_dict:
             mapping = kws
         elif kws:
-            mapping = _ChainMap(kws, mapping)
+            from collections import ChainMap
+            mapping = ChainMap(kws, mapping)
         # Helper function for .sub()
         def convert(mo):
             named = mo.group('named') or mo.group('braced')
@@ -170,10 +189,6 @@ class Template:
                     self.pattern)
         return ids
 
-# Initialize Template.pattern.  __init_subclass__() is automatically called
-# only for subclasses, not for the Template class itself.
-Template.__init_subclass__()
-
 
 ########################################################################
 # the Formatter class
@@ -212,19 +227,20 @@ class Formatter:
                 # this is some markup, find the object and do
                 #  the formatting
 
-                # handle arg indexing when empty field_names are given.
-                if field_name == '':
+                # handle arg indexing when empty field first parts are given.
+                field_first, _ = _string.formatter_field_name_split(field_name)
+                if field_first == '':
                     if auto_arg_index is False:
                         raise ValueError('cannot switch from manual field '
                                          'specification to automatic field '
                                          'numbering')
-                    field_name = str(auto_arg_index)
+                    field_name = str(auto_arg_index) + field_name
                     auto_arg_index += 1
-                elif field_name.isdigit():
+                elif isinstance(field_first, int):
                     if auto_arg_index:
-                        raise ValueError('cannot switch from manual field '
-                                         'specification to automatic field '
-                                         'numbering')
+                        raise ValueError('cannot switch from automatic field '
+                                         'numbering to manual field '
+                                         'specification')
                     # disable auto arg incrementing, if it gets
                     # used later on, then an exception will be raised
                     auto_arg_index = False

Lib/string/templatelib.py

@@ -0,0 +1,33 @@
+"""Support for template string literals (t-strings)."""
+
+t = t"{0}"
+Template = type(t)
+Interpolation = type(t.interpolations[0])
+del t
+
+def convert(obj, /, conversion):
+    """Convert *obj* using formatted string literal semantics."""
+    if conversion is None:
+        return obj
+    if conversion == 'r':
+        return repr(obj)
+    if conversion == 's':
+        return str(obj)
+    if conversion == 'a':
+        return ascii(obj)
+    raise ValueError(f'invalid conversion specifier: {conversion}')
+
+def _template_unpickle(*args):
+    import itertools
+
+    if len(args) != 2:
+        raise ValueError('Template expects tuple of length 2 to unpickle')
+
+    strings, interpolations = args
+    parts = []
+    for string, interpolation in itertools.zip_longest(strings, interpolations):
+        if string is not None:
+            parts.append(string)
+        if interpolation is not None:
+            parts.append(interpolation)
+    return Template(*parts)