diff --git a/implementations/python/preserves/text.py b/implementations/python/preserves/text.py
index d448126..424441b 100644
--- a/implementations/python/preserves/text.py
+++ b/implementations/python/preserves/text.py
@@ -312,10 +312,16 @@ def parse_with_annotations(bs, **kwargs):
     return Parser(input_buffer=bs, include_annotations=True, **kwargs).next()
 
 class Formatter(TextCodec):
-    def __init__(self, format_embedded=lambda x: x, indent=None):
+    def __init__(self,
+                 format_embedded=lambda x: x,
+                 indent=None,
+                 with_commas=False,
+                 trailing_comma=False):
         super(Formatter, self).__init__()
         self.indent_delta = 0 if indent is None else indent
         self.indent_distance = 0
+        self.with_commas = with_commas
+        self.trailing_comma = trailing_comma
         self.chunks = []
         self._format_embedded = format_embedded
 
@@ -362,9 +368,11 @@ class Formatter(TextCodec):
             self.write_indent()
             appender(vs[0])
             for v in vs[1:]:
+                if self.with_commas: self.chunks.append(',')
                 self.write_indent_space()
                 appender(v)
             self.indent_distance = self.indent_distance - self.indent_delta
+            if self.trailing_comma: self.chunks.append(',')
             self.write_indent()
         self.chunks.append(closer)
 
diff --git a/implementations/python/setup.py b/implementations/python/setup.py
index fcd39be..767b0ae 100644
--- a/implementations/python/setup.py
+++ b/implementations/python/setup.py
@@ -5,7 +5,7 @@ except ImportError:
 
 setup(
     name="preserves",
-    version="0.11.0",
+    version="0.12.0",
     author="Tony Garnock-Jones",
     author_email="tonyg@leastfixedpoint.com",
     license="Apache Software License",