Special-case None priority in place of -1

This extends priorities in both directions, uses slightly faster `is None`
check, makes it consistent with `interval` special-casing also to `None` and
makes lint able to use one simple `.type()` check in place of `.either()` one.

docs/source/configuration.rst

@@ -377,14 +377,13 @@ Themes
         can be aligned with the ``align`` property.
 
     ``priority``
-        Optional segment priority. Segments with priority ``-1`` (the 
-        default priority) will always be included, regardless of the width 
-        of the prompt/statusline.
+        Optional segment priority. Segments with priority ``None`` (the default 
+        priority, represented by ``null`` in json) will always be included, 
+        regardless of the width of the prompt/statusline.
 
-        If the priority is ``0`` or more, the segment may be removed if the 
+        If the priority is any number, the segment may be removed if the 
         prompt/statusline width is too small for all the segments to be 
-        rendered. A lower number means that the segment has a higher 
-        priority.
+        rendered. A lower number means that the segment has a higher priority.
 
         Segments are removed according to their priority, with low priority 
         segments being removed first.

powerline/lint/__init__.py

@@ -818,7 +818,7 @@ segments_spec = Spec().optional().list(
 		draw_soft_divider=Spec().type(bool).optional(),
 		draw_inner_divider=Spec().type(bool).optional(),
 		module=segment_module_spec(),
-		priority=Spec().either(Spec().cmp('eq', -1), Spec().cmp('ge', 0.0)).optional(),
+		priority=Spec().type(int, float, type(None)).optional(),
 		after=Spec().type(unicode).optional(),
 		before=Spec().type(unicode).optional(),
 		width=Spec().either(Spec().unsigned(), Spec().cmp('eq', 'auto')).optional(),

powerline/renderer.py

@@ -195,7 +195,7 @@ class Renderer(object):
 			return construct_returned_value(''.join([segment['_rendered_hl'] for segment in segments]) + self.hlstyle(), segments, output_raw)
 
 		# Create an ordered list of segments that can be dropped
-		segments_priority = [segment for segment in sorted(segments, key=lambda segment: segment['priority'], reverse=True) if segment['priority'] > 0]
+		segments_priority = [segment for segment in sorted(segments, key=lambda segment: segment['priority'], reverse=True) if segment['priority'] is not None]
 		while sum([segment['_len'] for segment in segments]) > width and len(segments_priority):
 			segments.remove(segments_priority[0])
 			segments_priority.pop(0)

powerline/segment.py

@@ -73,7 +73,7 @@ def gen_segment_getter(ext, path, theme_configs, default_module=None):
 			'contents_func': contents_func,
 			'contents': contents,
 			'args': get_key(segment, module, 'args', {}) if segment_type == 'function' else {},
-			'priority': segment.get('priority', -1),
+			'priority': segment.get('priority', None),
 			'draw_hard_divider': segment.get('draw_hard_divider', True),
 			'draw_soft_divider': segment.get('draw_soft_divider', True),
 			'draw_inner_divider': segment.get('draw_inner_divider', False),