Add concatenate(serial_comma=True) option (#30)

humanfriendly/tests.py

@@ -730,6 +730,8 @@ def test_concatenate(self):
         assert concatenate(['one', 'two', 'three']) == 'one, two and three'
         # Test the 'conjunction' option.
         assert concatenate(['one', 'two', 'three'], conjunction='or') == 'one, two or three'
+        # Test the 'serial_comma' option.
+        assert concatenate(['one', 'two', 'three'], serial_comma=True) == 'one, two, and three'
 
     def test_split(self):
         """Test :func:`humanfriendly.text.split()`."""

humanfriendly/text.py

@@ -93,7 +93,7 @@ def compact_empty_lines(text):
     return ''.join(lines)
 
 
-def concatenate(items, conjunction='and'):
+def concatenate(items, conjunction='and', serial_comma=False):
     """
     Concatenate a list of items in a human friendly way.
 
@@ -105,18 +105,28 @@ def concatenate(items, conjunction='and'):
 
         The word to use before the last item (a string, defaults to "and").
 
+    :param serial_comma:
+
+        :data:`True` to use a `serial comma`_, :data:`False` otherwise
+        (defaults to :data:`False`).
+
     :returns:
 
         A single string.
 
     >>> from humanfriendly.text import concatenate
     >>> concatenate(["eggs", "milk", "bread"])
     'eggs, milk and bread'
+
+    .. _serial comma: https://en.wikipedia.org/wiki/Serial_comma
     """
     items = list(items)
     if len(items) > 1:
-        last_item = items.pop()
-        return ' '.join([', '.join(items), conjunction, last_item])
+        final_item = items.pop()
+        formatted = ', '.join(items)
+        if serial_comma:
+            formatted += ','
+        return ' '.join([formatted, conjunction, final_item])
     elif items:
         return items[0]
     else: