Adding VI-mode in prompt

From the code it is apparent that if vi-mode is enabled, it should
display in the prompt. However, as the compare done is done against an
Enum class, it will always return False.

The solution is either to access the Enum's `.value` attribute, or to
compare it to the declared Enum value directly. The latter is likely
more readable.

IPython/terminal/prompts.py

@@ -1,102 +1,103 b''
 """Terminal input and output prompts."""
 
 from pygments.token import Token
 import sys
 
 from IPython.core.displayhook import DisplayHook
 
 from prompt_toolkit.formatted_text import fragment_list_width, PygmentsTokens
 from prompt_toolkit.shortcuts import print_formatted_text
+from prompt_toolkit.enums import EditingMode
 
 
 class Prompts(object):
     def __init__(self, shell):
         self.shell = shell
 
     def vi_mode(self):
-        if (getattr(self.shell.pt_app, 'editing_mode', None) == 'VI'
+        if (getattr(self.shell.pt_app, 'editing_mode', None) == EditingMode.VI
                 and self.shell.prompt_includes_vi_mode):
             return '['+str(self.shell.pt_app.app.vi_state.input_mode)[3:6]+'] '
         return ''
 
 
     def in_prompt_tokens(self):
         return [
             (Token.Prompt, self.vi_mode() ),
             (Token.Prompt, 'In ['),
             (Token.PromptNum, str(self.shell.execution_count)),
             (Token.Prompt, ']: '),
         ]
 
     def _width(self):
         return fragment_list_width(self.in_prompt_tokens())
 
     def continuation_prompt_tokens(self, width=None):
         if width is None:
             width = self._width()
         return [
             (Token.Prompt, (' ' * (width - 5)) + '...: '),
         ]
 
     def rewrite_prompt_tokens(self):
         width = self._width()
         return [
             (Token.Prompt, ('-' * (width - 2)) + '> '),
         ]
 
     def out_prompt_tokens(self):
         return [
             (Token.OutPrompt, 'Out['),
             (Token.OutPromptNum, str(self.shell.execution_count)),
             (Token.OutPrompt, ']: '),
         ]
 
 class ClassicPrompts(Prompts):
     def in_prompt_tokens(self):
         return [
             (Token.Prompt, '>>> '),
         ]
 
     def continuation_prompt_tokens(self, width=None):
         return [
             (Token.Prompt, '... ')
         ]
 
     def rewrite_prompt_tokens(self):
         return []
 
     def out_prompt_tokens(self):
         return []
 
 class RichPromptDisplayHook(DisplayHook):
     """Subclass of base display hook using coloured prompt"""
     def write_output_prompt(self):
         sys.stdout.write(self.shell.separate_out)
         # If we're not displaying a prompt, it effectively ends with a newline,
         # because the output will be left-aligned.
         self.prompt_end_newline = True
 
         if self.do_full_cache:
             tokens = self.shell.prompts.out_prompt_tokens()
             prompt_txt = ''.join(s for t, s in tokens)
             if prompt_txt and not prompt_txt.endswith('\n'):
                 # Ask for a newline before multiline output
                 self.prompt_end_newline = False
 
             if self.shell.pt_app:
                 print_formatted_text(PygmentsTokens(tokens),
                     style=self.shell.pt_app.app.style, end='',
                 )
             else:
                 sys.stdout.write(prompt_txt)
 
     def write_format_data(self, format_dict, md_dict=None) -> None:
         if self.shell.mime_renderers:
 
             for mime, handler in self.shell.mime_renderers.items():
                 if mime in format_dict:
                     handler(format_dict[mime], None)
                     return
                 
         super().write_format_data(format_dict, md_dict)