Fix bug #548 - Transpose when empty line crashes

wevial · wevial · commit c08b42d6dcc3 · 2015-08-26T15:39:12.000-04:00
diff --git a/bpython/curtsiesfrontend/manual_readline.py b/bpython/curtsiesfrontend/manual_readline.py
@@ -280,11 +280,13 @@ def yank_prev_killed_text(cursor_offset, line, cut_buffer):
 
 @edit_keys.on(config='transpose_chars_key')
 def transpose_character_before_cursor(cursor_offset, line):
+    if cursor_offset == 0:
+        return cursor_offset, line
     return (min(len(line), cursor_offset + 1),
-            line[:cursor_offset-1] +
+            line[:cursor_offset - 1] +
             (line[cursor_offset] if len(line) > cursor_offset else '') +
             line[cursor_offset - 1] +
-            line[cursor_offset+1:])
+            line[cursor_offset + 1:])
 
 
 @edit_keys.on('<Esc+t>')
diff --git a/bpython/test/test_manual_readline.py b/bpython/test/test_manual_readline.py
@@ -201,6 +201,16 @@ def test_transpose_character_before_cursor(self):
                          "adf s|asdf",
                          "adf as|sdf"], transpose_character_before_cursor)
 
+    def test_transpose_empty_line(self):
+        self.assertEquals(transpose_character_before_cursor(0, ''),
+                (0,''))
+
+    def test_transpose_first_character(self):
+        self.assertEquals(transpose_character_before_cursor(0, 'a'),
+                transpose_character_before_cursor(0, 'a'))
+        self.assertEquals(transpose_character_before_cursor(0, 'as'),
+                transpose_character_before_cursor(0, 'as'))
+
     def test_transpose_word_before_cursor(self):
         pass
 
