Support terminal types, such as kermit and avatar, that use bytes 127…

…-255 in their escape sequences. Close erikrose#47.

README.rst

@@ -441,6 +441,8 @@ Version History
   * Add ``fullscreen()`` and ``hidden_cursor()`` to the auto-generated docs.
   * Fall back to ``LINES`` and ``COLUMNS`` environment vars to find height and
     width. (jquast)
+  * Support terminal types, such as kermit and avatar, that use bytes 127-255
+    in their escape sequences. (jquast)
 
 1.5.1
   * Clean up fabfile, removing the redundant ``test`` command.

blessings/__init__.py

@@ -376,10 +376,8 @@ def _resolve_capability(self, atom):
         """
         code = tigetstr(self._sugar.get(atom, atom))
         if code:
-            # We can encode escape sequences as UTF-8 because they never
-            # contain chars > 127, and UTF-8 never changes anything within that
-            # range..
-            return code.decode('utf-8')
+            # See the comment in ParametrizingString for why this is latin1.
+            return code.decode('latin1')
         return u''
 
     def _resolve_color(self, color):
@@ -448,7 +446,15 @@ def __call__(self, *args):
             # Re-encode the cap, because tparm() takes a bytestring in Python
             # 3. However, appear to be a plain Unicode string otherwise so
             # concats work.
-            parametrized = tparm(self.encode('utf-8'), *args).decode('utf-8')
+            #
+            # We use *latin1* encoding so that bytes emitted by tparm are
+            # encoded to their native value: some terminal kinds, such as
+            # 'avatar' or 'kermit', emit 8-bit bytes in range 0x7f to 0xff.
+            # latin1 leaves these values unmodified in their conversion to
+            # unicode byte values. The terminal emulator will "catch" and
+            # handle these values, even if emitting utf8-encoded text, where
+            # these bytes would otherwise be illegal utf8 start bytes.
+            parametrized = tparm(self.encode('latin1'), *args).decode('latin1')
             return (parametrized if self._normal is None else
                     FormattingString(parametrized, self._normal))
         except curses.error:

blessings/tests.py

@@ -28,12 +28,12 @@
 
 def unicode_cap(cap):
     """Return the result of ``tigetstr`` except as Unicode."""
-    return tigetstr(cap).decode('utf-8')
+    return tigetstr(cap).decode('latin1')
 
 
 def unicode_parm(cap, *parms):
     """Return the result of ``tparm(tigetstr())`` except as Unicode."""
-    return tparm(tigetstr(cap), *parms).decode('utf-8')
+    return tparm(tigetstr(cap), *parms).decode('latin1')
 
 
 def test_capability():