Ensure only printable keys added to footer

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Fixed
+
+- Ensure only printable characters are used as key_display https://github.com/Textualize/textual/pull/1361
 
 ## [0.6.0] - 2022-12-11
 

docs/examples/widgets/footer.py

@@ -12,6 +12,7 @@ class FooterApp(App):
             description="Show help screen",
             key_display="?",
         ),
+        Binding(key="delete", action="delete", description="Delete the thing"),
         Binding(key="j", action="down", description="Scroll down", show=False),
     ]
 

src/textual/keys.py

@@ -245,9 +245,14 @@ def _get_key_display(key: str) -> str:
         return display_alias
 
     original_key = REPLACED_KEYS.get(key, key)
+    upper_original = original_key.upper().replace("_", " ")
     try:
-        unicode_character = unicodedata.lookup(original_key.upper().replace("_", " "))
+        unicode_character = unicodedata.lookup(upper_original)
     except KeyError:
-        return original_key.upper()
+        return upper_original
 
-    return unicode_character
+    # Check if printable. `delete` for example maps to a control sequence
+    # which we don't want to write to the terminal.
+    if unicode_character.isprintable():
+        return unicode_character
+    return upper_original