Add narrative docs for customizing enter behavior.

see  #10500
closes  #10503

docs/source/config/details.rst

@@ -1,230 +1,272 b''
 =======================
 Specific config details
 =======================
 
 .. _custom_prompts:
 
 Custom Prompts
 ==============
 
 .. versionchanged:: 5.0
 
 From IPython 5, prompts are produced as a list of Pygments tokens, which are
 tuples of (token_type, text). You can customise prompts by writing a method
 which generates a list of tokens.
 
 There are four kinds of prompt:
 
 * The **in** prompt is shown before the first line of input
   (default like ``In [1]:``).
 * The **continuation** prompt is shown before further lines of input
   (default like ``...:``).
 * The **rewrite** prompt is shown to highlight how special syntax has been
   interpreted (default like ``----->``).
 * The **out** prompt is shown before the result from evaluating the input
   (default like ``Out[1]:``).
 
 Custom prompts are supplied together as a class. If you want to customise only
 some of the prompts, inherit from :class:`IPython.terminal.prompts.Prompts`,
 which defines the defaults. The required interface is like this:
 
 .. class:: MyPrompts(shell)
 
    Prompt style definition. *shell* is a reference to the
    :class:`~.TerminalInteractiveShell` instance.
 
    .. method:: in_prompt_tokens(cli=None)
                continuation_prompt_tokens(self, cli=None, width=None)
                rewrite_prompt_tokens()
                out_prompt_tokens()
 
       Return the respective prompts as lists of ``(token_type, text)`` tuples.
 
       For continuation prompts, *width* is an integer representing the width of
       the prompt area in terminal columns.
 
       *cli*, where used, is the prompt_toolkit ``CommandLineInterface`` instance.
       This is mainly for compatibility with the API prompt_toolkit expects.
 
 Here is an example Prompt class that will show the current working directory
 in the input prompt:
 
 .. code-block:: python
 
     from IPython.terminal.prompts import Prompts, Token
     import os
 
     class MyPrompt(Prompts):
          def in_prompt_tokens(self, cli=None):
              return [(Token, os.getcwd()),
                      (Token.Prompt, ' >>>')]
 
 To set the new prompt, assign it to the ``prompts`` attribute of the IPython
 shell:
 
 .. code-block:: python
 
     In [2]: ip = get_ipython()
        ...: ip.prompts = MyPrompt(ip)
 
     /home/bob >>> # it works
 
 See ``IPython/example/utils/cwd_prompt.py`` for an example of how to write an
 extensions to customise prompts.
 
 Inside IPython or in a startup script, you can use a custom prompts class
 by setting ``get_ipython().prompts`` to an *instance* of the class.
 In configuration, ``TerminalInteractiveShell.prompts_class`` may be set to
 either the class object, or a string of its full importable name.
 
 To include invisible terminal control sequences in a prompt, use
 ``Token.ZeroWidthEscape`` as the token type. Tokens with this type are ignored
 when calculating the width.
 
 Colours in the prompt are determined by the token types and the highlighting
 style; see below for more details. The tokens used in the default prompts are
 ``Prompt``, ``PromptNum``, ``OutPrompt`` and ``OutPromptNum``.
 
 .. _termcolour:
 
 Terminal Colors
 ===============
 
 .. versionchanged:: 5.0
 
 There are two main configuration options controlling colours.
 
 ``InteractiveShell.colors`` sets the colour of tracebacks and object info (the
 output from e.g. ``zip?``). It may also affect other things if the option below
 is set to ``'legacy'``. It has four case-insensitive values:
 ``'nocolor', 'neutral', 'linux', 'lightbg'``. The default is *neutral*, which
 should be legible on either dark or light terminal backgrounds. *linux* is
 optimised for dark backgrounds and *lightbg* for light ones.
 
 ``TerminalInteractiveShell.highlighting_style`` determines prompt colours and
 syntax highlighting. It takes the name (as a string) or class (as a subclass of
 ``pygments.style.Style``) of a Pygments style, or the special value ``'legacy'``
 to pick a style in accordance with ``InteractiveShell.colors``.
 
 You can see the Pygments styles available on your system by running::
 
     import pygments
     list(pygments.styles.get_all_styles())
 
 Additionally, ``TerminalInteractiveShell.highlighting_style_overrides`` can override
 specific styles in the highlighting. It should be a dictionary mapping Pygments
 token types to strings defining the style. See `Pygments' documentation
 <http://pygments.org/docs/styles/#creating-own-styles>`__ for the language used
 to define styles.
 
 Colors in the pager
 -------------------
 
 On some systems, the default pager has problems with ANSI colour codes.
 To configure your default pager to allow these:
 
 1. Set the environment PAGER variable to ``less``.
 2. Set the environment LESS variable to ``-r`` (plus any other options
    you always want to pass to less by default). This tells less to
    properly interpret control sequences, which is how color
    information is given to your terminal.
 
 .. _editors:
 
 Editor configuration
 ====================
 
 IPython can integrate with text editors in a number of different ways:
 
 * Editors (such as `(X)Emacs`_, vim_ and TextMate_) can
   send code to IPython for execution.
 
 * IPython's ``%edit`` magic command can open an editor of choice to edit
   a code block.
 
 The %edit command (and its alias %ed) will invoke the editor set in your
 environment as :envvar:`EDITOR`. If this variable is not set, it will default
 to vi under Linux/Unix and to notepad under Windows. You may want to set this
 variable properly and to a lightweight editor which doesn't take too long to
 start (that is, something other than a new instance of Emacs). This way you
 can edit multi-line code quickly and with the power of a real editor right
 inside IPython.
 
 You can also control the editor by setting :attr:`TerminalInteractiveShell.editor`
 in :file:`ipython_config.py`.
 
 Vim
 ---
 
 Paul Ivanov's `vim-ipython <https://github.com/ivanov/vim-ipython>`_ provides
 powerful IPython integration for vim.
 
 .. _emacs:
 
 (X)Emacs
 --------
 
 If you are a dedicated Emacs user, and want to use Emacs when IPython's
 ``%edit`` magic command is called you should set up the Emacs server so that
 new requests are handled by the original process. This means that almost no
 time is spent in handling the request (assuming an Emacs process is already
 running). For this to work, you need to set your EDITOR environment variable
 to 'emacsclient'. The code below, supplied by Francois Pinard, can then be
 used in your :file:`.emacs` file to enable the server:
 
 .. code-block:: common-lisp
 
     (defvar server-buffer-clients)
     (when (and (fboundp 'server-start) (string-equal (getenv "TERM") 'xterm))
       (server-start)
       (defun fp-kill-server-with-buffer-routine ()
         (and server-buffer-clients (server-done)))
       (add-hook 'kill-buffer-hook 'fp-kill-server-with-buffer-routine))
 
 Thanks to the work of Alexander Schmolck and Prabhu Ramachandran,
 currently (X)Emacs and IPython get along very well in other ways.
 
 With (X)EMacs >= 24, You can enable IPython in python-mode with:
 
 .. code-block:: common-lisp
 
     (require 'python)
     (setq python-shell-interpreter "ipython")
 
 .. _`(X)Emacs`: http://www.gnu.org/software/emacs/
 .. _TextMate: http://macromates.com/
 .. _vim: http://www.vim.org/
 
 .. _custom_keyboard_shortcuts:
 
 Keyboard Shortcuts
 ==================
 
 .. versionchanged:: 5.0
 
 You can customise keyboard shortcuts for terminal IPython. Put code like this in
 a :ref:`startup file <startup_files>`::
 
     from IPython import get_ipython
     from prompt_toolkit.enums import DEFAULT_BUFFER
     from prompt_toolkit.keys import Keys
     from prompt_toolkit.filters import HasFocus, HasSelection, ViInsertMode, EmacsInsertMode
 
     ip = get_ipython()
     insert_mode = ViInsertMode() | EmacsInsertMode()
 
     def insert_unexpected(event):
         buf = event.current_buffer
         buf.insert_text('The Spanish Inquisition')
 
     # Register the shortcut if IPython is using prompt_toolkit
     if getattr(ip, 'pt_cli'):
         registry = ip.pt_cli.application.key_bindings_registry
         registry.add_binding(Keys.ControlN,
                          filter=(HasFocus(DEFAULT_BUFFER)
                                  & ~HasSelection()
                                  & insert_mode))(insert_unexpected)
 
 For more information on filters and what you can do with the ``event`` object,
 `see the prompt_toolkit docs
 <http://python-prompt-toolkit.readthedocs.io/en/latest/pages/building_prompts.html#adding-custom-key-bindings>`__.
+
+
+Enter to execute
+----------------
+
+In the Terminal IPython shell – which by default use the ``prompt_toolkit``
+interface, the semantic of pressing the :kbd:`Enter` key can be ambiguous, in
+some case :kbd:`Enter` should execute code, and in others it should add a new
+line. IPython is using some heuristics to decide whether to execute or insert a
+new line at cursor position. For example, if we detect that the current code is
+not valid Python, then the user is likely editing code and the right behavior is
+to likely to insert a new line. If the current code is a simple statement like
+`ord('*')`, then the right behavior is likely to execute. Though the exact
+desired semantics often varies from users to users.
+
+As the exact behavior of :kbd:`Enter` is subject to disagreement, it has been
+special cased in order for users to completely configure the behavior they like.
+Hence you can have enter to simply alway execute code, if you prefer more fancy
+behavior : start your coffee machine on even days of odd month. You'll have to
+get your hands dirty and read prompt_toolkit and IPython documentation though.
+See :ghpull:`10500`, set the `c.TerminalInteractiveShell.handle_return` option
+and get inspiration from the following example that insert new lines only after
+a pipe (``|``). Place the following in your configuration to do so::
+
+    def new_line_after_pipe(shell):
+        # shell is the same as get_ipython()
+        def insert(event):
+            """When the user presses return, insert"""
+            b = event.current_buffer
+            d = b.document
+
+            # if character before cursor is `|`
+            if d.text[d.cursor_position-1] == '|':
+                # insert a new line
+                b.insert_text('\n')
+            else:
+                # otherwise execute.
+                b.accept_action.validate_and_handle(event.cli, b)
+        return insert
+
+    # set the heuristic to our new function
+    c.TerminalInteractiveShell.handle_return = new_line_after_pipe