Additional listbox functionality

* Add title_align as a new keyword argument to construct a ListBox.  It
  allows justifying a ListBox to the left or right in addition to
  centering it.  This can be useful for constructing columns out of
  ListBoxes.
* Implement borderless sides.  If a ListBox is created with lines or
  corners set to the empty string then do not create a border element
  for them. This allows adjoining list boxes to share a single border,
  or two ListBoxes to seamlessly merge into one another.

Fixes #211

1 files changed, 67 insertions, 26 deletions

diff --git a/urwid/graphics.py b/urwid/graphics.py
index cb852b0..3d2046b 100755
--- a/urwid/graphics.py
+++ b/urwid/graphics.py
@@ -96,7 +96,7 @@ class BigText(Widget):
 
 class LineBox(WidgetDecoration, WidgetWrap):
 
-    def __init__(self, original_widget, title="",
+    def __init__(self, original_widget, title="", title_align="center",
                  tlcorner=u'┌', tline=u'─', lline=u'│',
                  trcorner=u'┐', blcorner=u'└', rline=u'│',
                  bline=u'─', brcorner=u'┘'):
@@ -106,6 +106,9 @@ class LineBox(WidgetDecoration, WidgetWrap):
         Use 'title' to set an initial title text with will be centered
         on top of the box.
 
+        Use `title_align` to align the title to the 'left', 'right', or 'center'.
+        The default is 'center'.
+
         You can also override the widgets used for the lines/corners:
             tline: top line
             bline: bottom line
@@ -116,37 +119,73 @@ class LineBox(WidgetDecoration, WidgetWrap):
             blcorner: bottom left corner
             brcorner: bottom right corner
 
+        If empty string is specified for one of the lines/corners, then no
+        character will be output there.  This allows for seamless use of
+        adjoining LineBoxes.
         """
 
-        tline, bline = Divider(tline), Divider(bline)
-        lline, rline = SolidFill(lline), SolidFill(rline)
+        if tline:
+            tline = Divider(tline)
+        if bline:
+            bline = Divider(bline)
+        if lline:
+            lline = SolidFill(lline)
+        if rline:
+            rline = SolidFill(rline)
         tlcorner, trcorner = Text(tlcorner), Text(trcorner)
         blcorner, brcorner = Text(blcorner), Text(brcorner)
 
+        if not tline and title:
+            raise ValueError('Cannot have a title when tline is empty string')
+
         self.title_widget = Text(self.format_title(title))
-        self.tline_widget = Columns([
-            tline,
-            ('flow', self.title_widget),
-            tline,
-        ])
-
-        top = Columns([
-            ('fixed', 1, tlcorner),
-            self.tline_widget,
-            ('fixed', 1, trcorner)
-        ])
-
-        middle = Columns([
-            ('fixed', 1, lline),
-            original_widget,
-            ('fixed', 1, rline),
-        ], box_columns=[0, 2], focus_column=1)
-
-        bottom = Columns([
-            ('fixed', 1, blcorner), bline, ('fixed', 1, brcorner)
-        ])
-
-        pile = Pile([('flow', top), middle, ('flow', bottom)], focus_item=1)
+
+        if tline:
+            if title_align not in ('left', 'center', 'right'):
+                raise ValueError('title_align must be one of "left", "right", or "center"')
+            if title_align == 'left':
+                tline_widgets = [('flow', self.title_widget), tline]
+            else:
+                tline_widgets = [tline, ('flow', self.title_widget)]
+                if title_align == 'center':
+                    tline_widgets.append(tline)
+            self.tline_widget = Columns(tline_widgets)
+            top = Columns([
+                ('fixed', 1, tlcorner),
+                self.tline_widget,
+                ('fixed', 1, trcorner)
+            ])
+
+        else:
+            self.tline_widget = None
+            top = None
+
+        middle_widgets = []
+        if lline:
+            middle_widgets.append(('fixed', 1, lline))
+        middle_widgets.append(original_widget)
+        focus_col = len(middle_widgets) - 1
+        if rline:
+            middle_widgets.append(('fixed', 1, rline))
+
+        middle = Columns(middle_widgets,
+                box_columns=[0, 2], focus_column=focus_col)
+
+        if bline:
+            bottom = Columns([
+                ('fixed', 1, blcorner), bline, ('fixed', 1, brcorner)
+            ])
+        else:
+            bottom = None
+
+        pile_widgets = []
+        if top:
+            pile_widgets.append(('flow', top))
+        pile_widgets.append(middle)
+        focus_pos = len(pile_widgets) - 1
+        if bottom:
+            pile_widgets.append(('flow', bottom))
+        pile = Pile(pile_widgets, focus_item=focus_pos)
 
         WidgetDecoration.__init__(self, original_widget)
         WidgetWrap.__init__(self, pile)
@@ -158,6 +197,8 @@ class LineBox(WidgetDecoration, WidgetWrap):
             return ""
 
     def set_title(self, text):
+        if not self.title_widget:
+            raise ValueError('Cannot set title when tline is unset')
         self.title_widget.set_text(self.format_title(text))
         self.tline_widget._invalidate()