document set_class

Author: willmcgugan

docs/guide/CSS.md

@@ -297,6 +297,7 @@ Unlike the `id` attribute, a widget's classes can be changed after the widget wa
 - [remove_class()][textual.dom.DOMNode.remove_class] Removes class name(s) from a widget.
 - [toggle_class()][textual.dom.DOMNode.toggle_class] Removes a class name if it is present, or adds the name if it's not already present.
 - [has_class()][textual.dom.DOMNode.has_class] Checks if one or more classes are set on a widget.
+- [set_class()][textual.css.query.DOMQuery.set_class] Sets or removes a class dependant on a boolean.
 - [classes][textual.dom.DOMNode.classes] Is a frozen set of the class(es) set on a widget.
 
 

src/textual/dom.py

@@ -1665,6 +1665,17 @@ def has_class(self, *class_names: str) -> bool:
     def set_class(self, add: bool, *class_names: str, update: bool = True) -> Self:
         """Add or remove class(es) based on a condition.
 
+        This can condense the four lines required to implement the equivalent branch into a single line.
+
+        Example:
+            ```python
+            #if foo:
+            #    self.add_class("-foo")
+            #else:
+            #    self.remove_class("-foo")
+            self.set_class(foo, "-foo")
+            ```
+
         Args:
             add: Add the classes if True, otherwise remove them.
             update: Also update styles.