Index: Doc/library/string.rst
===================================================================
--- Doc/library/string.rst	(révision 88911)
+++ Doc/library/string.rst	(copie de travail)
@@ -650,9 +650,10 @@
 these rules.  The methods of :class:`Template` are:
 
 
-.. class:: Template(template)
+.. class:: Template(template, default=None)
 
-   The constructor takes a single argument which is the template string.
+   The constructor takes two arguments, the first is the template string and
+   the second (optional) is a mapping which gives default values.
 
 
    .. method:: substitute(mapping, **kwds)
@@ -667,10 +668,11 @@
    .. method:: safe_substitute(mapping, **kwds)
 
       Like :meth:`substitute`, except that if placeholders are missing from
-      *mapping* and *kwds*, instead of raising a :exc:`KeyError` exception, the
-      original placeholder will appear in the resulting string intact.  Also,
-      unlike with :meth:`substitute`, any other appearances of the ``$`` will
-      simply return ``$`` instead of raising :exc:`ValueError`.
+      *mapping*, *kwds* and the default values given to the constructor,
+      instead of raising a :exc:`KeyError` exception, the original placeholder
+      will appear in the resulting string intact.  Also, unlike with
+      :meth:`substitute`, any other appearances of the ``$`` will simply
+      return ``$`` instead of raising :exc:`ValueError`.
 
       While other exceptions may still occur, this method is called "safe"
       because substitutions always tries to return a usable string instead of
@@ -679,17 +681,24 @@
       templates containing dangling delimiters, unmatched braces, or
       placeholders that are not valid Python identifiers.
 
-   :class:`Template` instances also provide one public data attribute:
+   :class:`Template` instances also provide two public data attributes:
 
    .. attribute:: template
 
       This is the object passed to the constructor's *template* argument.  In
       general, you shouldn't change it, but read-only access is not enforced.
+   
+   .. attribute:: default
+      
+      This is the optional mapping passed as the *default* argument to the
+      contructor.
 
 Here is an example of how to use a Template:
 
    >>> from string import Template
-   >>> s = Template('$who likes $what')
+   >>> s = Template('$who likes $what', default={"who":"dennis"})
+   >>> s.substitute(what='vanilla cakes')
+   'dennis likes vanilla cakes'
    >>> s.substitute(who='tim', what='kung pao')
    'tim likes kung pao'
    >>> d = dict(who='tim')
@@ -703,6 +712,8 @@
    KeyError: 'what'
    >>> Template('$who likes $what').safe_substitute(d)
    'tim likes $what'
+   >>> Template('$who likes $what', default={"what":"red cars"}).substitute(d)
+   'tim likes red cars'
 
 Advanced usage: you can derive subclasses of :class:`Template` to customize the
 placeholder syntax, delimiter character, or the entire regular expression used
Index: Lib/string.py
===================================================================
--- Lib/string.py	(révision 88911)
+++ Lib/string.py	(copie de travail)
@@ -77,8 +77,9 @@
     idpattern = r'[_a-z][_a-z0-9]*'
     flags = _re.IGNORECASE
 
-    def __init__(self, template):
+    def __init__(self, template, default=None):
         self.template = template
+        self.default = default if default is not None else {}
 
     # Search for $$, $identifier, ${identifier}, and any bare $'s
 
@@ -97,12 +98,14 @@
     def substitute(self, *args, **kws):
         if len(args) > 1:
             raise TypeError('Too many positional arguments')
+        
+        mapping = self.default
         if not args:
-            mapping = kws
+            mapping.update(kws)
         elif kws:
-            mapping = ChainMap(kws, args[0])
+            mapping.update(ChainMap(kws, args[0]))
         else:
-            mapping = args[0]
+            mapping.update(args[0])
         # Helper function for .sub()
         def convert(mo):
             # Check the most common path first.