Add example for setting a theme (#1497)

* Draft example for setting a theme

* Fix typos

* Add some more elements to the custom theme

* Added in a custom self.doc_leader

* Add in setting background color for one style to make it discoverable that this is an option

* Change some styles to show off different options

* Add comments about how colors can be defined

* Fix typo

* Overrode "traceback.exc_type"

Author: tleonhardt

examples/rich_theme.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+"""A simple example of setting a custom theme for a cmd2 application."""
+
+from rich.style import Style
+
+import cmd2
+import cmd2.rich_utils as ru
+from cmd2 import Cmd2Style, Color
+
+
+class ThemedApp(cmd2.Cmd):
+    """A simple cmd2 application with a custom theme."""
+
+    def __init__(self, *args, **kwargs):
+        """Initialize the application."""
+        super().__init__(*args, **kwargs)
+        self.intro = "This is a themed application. Try the 'theme_show' command."
+
+        # Set text which prints right before all of the help tables are listed.
+        self.doc_leader = "Welcome to this glorious help ..."
+
+        # Create a custom theme
+        # Colors can come from the cmd2.color.Color StrEnum class, be RGB hex values, or
+        # be any of the rich standard colors: https://rich.readthedocs.io/en/stable/appendix/colors.html
+        custom_theme = {
+            Cmd2Style.SUCCESS: Style(color=Color.GREEN),  # Use color from cmd2 Color class
+            Cmd2Style.WARNING: Style(color=Color.ORANGE1),
+            Cmd2Style.ERROR: Style(color=Color.PINK1),
+            Cmd2Style.HELP_HEADER: Style(color=Color.CYAN, bgcolor="#44475a"),
+            Cmd2Style.HELP_LEADER: Style(color="#f8f8f2", bgcolor="#282a36"),  # use RGB hex colors
+            Cmd2Style.TABLE_BORDER: Style(color="turquoise2"),  # use a rich standard color
+            "traceback.exc_type": Style(color=Color.RED, bgcolor=Color.LIGHT_YELLOW3),
+            "argparse.args": Style(color=Color.AQUAMARINE3, underline=True),
+            "inspect.attr": Style(color=Color.DARK_GOLDENROD, bold=True),
+        }
+        ru.set_theme(custom_theme)
+
+    @cmd2.with_category("Theme Commands")
+    def do_theme_show(self, _: cmd2.Statement):
+        """Showcases the custom theme by printing messages with different styles."""
+        # NOTE: Using soft_wrap=False will ensure display looks correct when background colors are part of the style
+        self.poutput("This is a basic output message.")
+        self.psuccess("This is a success message.", soft_wrap=False)
+        self.pwarning("This is a warning message.", soft_wrap=False)
+        self.perror("This is an error message.", soft_wrap=False)
+        self.pexcept(ValueError("This is a dummy ValueError exception."))
+
+
+if __name__ == "__main__":
+    import sys
+
+    app = ThemedApp()
+    sys.exit(app.cmdloop())