Autoformat with black

IPython/terminal/interactiveshell.py

@@ -87,6 +87,14 @@ def get_default_editor():
 
 _use_simple_prompt = ('IPY_TEST_SIMPLE_PROMPT' in os.environ) or (not _is_tty)
 
+def black_reformat_handler(text_before_cursor):
+    import black
+    formatted_text = black.format_str(text_before_cursor, mode=black.FileMode())
+    if not text_before_cursor.endswith('\n') and formatted_text.endswith('\n'):
+       formatted_text = formatted_text[:-1]
+    return formatted_text
+
+
 class TerminalInteractiveShell(InteractiveShell):
     space_for_menu = Integer(6, help='Number of line at the bottom of the screen '
                                      'to reserve for the completion menu'
@@ -120,6 +128,11 @@ def debugger_cls(self):
         help="Shortcut style to use at the prompt. 'vi' or 'emacs'.",
     ).tag(config=True)
 
+    autoformatter = Unicode(None,
+        help="Autoformatter to reformat Terminal code. Can be `'black'` or `None`",
+        allow_none=True
+    ).tag(config=True)
+
     mouse_support = Bool(False,
         help="Enable mouse support in the prompt\n(Note: prevents selecting text with the mouse)"
     ).tag(config=True)
@@ -150,6 +163,16 @@ def _editing_mode(self, change):
         if self.pt_app:
             self.pt_app.editing_mode = u_mode
 
+    @observe('autoformatter')
+    def _autoformatter_changed(self, change):
+        formatter = change.new
+        if formatter is None:
+            self.reformat_handler = lambda x:x
+        elif formatter == 'black':
+            self.reformat_handler = black_reformat_handler
+        else:
+            raise ValueError
+
     @observe('highlighting_style')
     @observe('colors')
     def _highlighting_style_changed(self, change):

IPython/terminal/shortcuts.py

@@ -44,6 +44,15 @@ def create_ipython_shortcuts(shell):
                             & insert_mode
                         ))(return_handler)
 
+    def reformat_and_execute(event):
+        reformat_text_before_cursor(event.current_buffer, event.current_buffer.document, shell)
+        event.current_buffer.validate_and_handle()
+
+    kb.add('escape', 'enter', filter=(has_focus(DEFAULT_BUFFER)
+                            & ~has_selection
+                            & insert_mode
+                                      ))(reformat_and_execute)
+
     kb.add('c-\\')(force_exit)
 
     kb.add('c-p', filter=(vi_insert_mode & has_focus(DEFAULT_BUFFER))
@@ -86,7 +95,17 @@ def create_ipython_shortcuts(shell):
     return kb
 
 
+def reformat_text_before_cursor(buffer, document, shell):
+    text = buffer.delete_before_cursor(len(document.text[:document.cursor_position]))
+    try:
+        formatted_text = shell.reformat_handler(text)
+        buffer.insert_text(formatted_text)
+    except Exception as e:
+        buffer.insert_text(text)
+
+
 def newline_or_execute_outer(shell):
+
     def newline_or_execute(event):
         """When the user presses return, insert a newline or execute the code."""
         b = event.current_buffer
@@ -107,7 +126,12 @@ def newline_or_execute(event):
         else:
             check_text = d.text[:d.cursor_position]
         status, indent = shell.check_complete(check_text)
-
+
+        # if all we have after the cursor is whitespace: reformat current text
+        # before cursor
+        after_cursor = d.text[d.cursor_position:]
+        if not after_cursor.strip():
+            reformat_text_before_cursor(b, d, shell)
         if not (d.on_last_line or
                 d.cursor_position_row >= d.line_count - d.empty_line_count_at_the_end()
                 ):
@@ -118,6 +142,7 @@ def newline_or_execute(event):
             return
 
         if (status != 'incomplete') and b.accept_handler:
+            reformat_text_before_cursor(b, d, shell)
             b.validate_and_handle()
         else:
             if shell.autoindent:

docs/source/whatsnew/pr/autoformatting.rst

@@ -0,0 +1,24 @@
+Code autoformatting
+===================
+
+The IPython terminal can now auto format your code just before entering a new
+line or executing a command. To do so use the
+``--TerminalInteractiveShell.autoformatter`` option and set it to ``'black'``;
+if black is installed IPython will use black to format your code when possible. 
+
+IPython cannot always properly format your code; in particular it will
+auto formatting with *black* will only work if:
+
+   - Your code does not contains magics or special python syntax. 
+
+   - There is no code after your cursor. 
+
+The Black API is also still in motion; so this may not work with all versions of
+black. 
+
+It should be possible to register custom reformatter, though the API is till in
+flux. 
+
+
+
+