Don't update widgets if they're uninterested

3 files changed, 20 insertions, 5 deletions

diff --git a/NEWS b/NEWS
index 3365fab..be4d334 100644
--- a/NEWS
+++ b/NEWS
@@ -11,6 +11,11 @@ Version 0.30, released UNRELEASED
 * New method `ttystatus.TerminalStatus.get_terminal_size` returns
   terminal width and height.
 
+* Speed up updates by not updating widgets if they aren't interested
+  in the variable that got changed. This only works for widgets added
+  with the `format` method, but that should be all of them for anyone
+  not liking verbose, tedious code.
+
 Version 0.29, released 2015-10-10
 ---------------------------------
 
diff --git a/ttystatus/fmt.py b/ttystatus/fmt.py
index 5ad7994..ec5b18f 100644
--- a/ttystatus/fmt.py
+++ b/ttystatus/fmt.py
@@ -46,12 +46,16 @@ def parse(fmt):
         m = pat.match(fmt)
         if m:
             if prefix:
-                result.append(ttystatus.Literal(prefix))
+                literal = ttystatus.Literal(prefix)
+                literal.interested_in = []
+                result.append(literal)
                 prefix = ''
             klass = getattr(ttystatus, m.group('class'))
             argnames = m.group('args').split(',')
             argnames = [x for x in argnames if x]
-            result.append(klass(*argnames))
+            widget = klass(*argnames)
+            widget.interested_in = argnames
+            result.append(widget)
             fmt = fmt[m.end():]
         elif fmt.startswith('%%'):
             prefix += '%'
@@ -61,5 +65,7 @@ def parse(fmt):
             fmt = fmt[1:]
 
     if prefix:
-        result.append(ttystatus.Literal(prefix))
+        literal = ttystatus.Literal(prefix)
+        literal.interested_in = []
+        result.append(literal)
     return result
diff --git a/ttystatus/status.py b/ttystatus/status.py
index df45ebc..fe90b96 100644
--- a/ttystatus/status.py
+++ b/ttystatus/status.py
@@ -46,6 +46,8 @@ class TerminalStatus(object):
         if not self._widget_rows:
             self._widget_rows = [[]]
         self._widget_rows[-1].append(widget)
+        if not hasattr(widget, 'interested_in'):
+            widget.interested_in = None
 
     def start_new_line(self):  # pragma: no cover
         '''Start a new line of widgets.'''
@@ -79,7 +81,8 @@ class TerminalStatus(object):
     def clear(self):
         '''Remove all widgets.'''
         self._widget_rows = []
-        self._values = dict()
+        self._values = {}
+        self._interested_in = {}
         self._m.clear()
 
     def __getitem__(self, key):
@@ -95,7 +98,8 @@ class TerminalStatus(object):
         self._values[key] = value
         for row in self._widget_rows:
             for w in row:
-                w.update(self)
+                if w.interested_in is None or key in w.interested_in:
+                    w.update(self)
         if self._m.is_enabled() and self._m.time_to_write():
             self._write()