.. rst3: filename: html\cheatsheet.html

#################
Leo's Cheat Sheet
#################

This Cheat Sheet contains a summary of many of Leo's important features.
**Important**: The easiest way to find documentation is to search LeoDocs.leo.

.. contents:: Contents
    :depth: 4
    :local:

Key bindings
++++++++++++

Selecting outline nodes
***********************

When focus is in the outline pane::

    Right-arrow (expand-and-go-right)
    Left-arrow (contract-or-go-left)
    Up-arrow (goto-prev-visible) 
    Down-arrow (goto-next-visible)
    
Regardless of focus::

    Alt-Home (goto-first-visible-node) 
    Alt-End (goto-last-visible-node)
    Alt-Right-arrow (expand-and-go-right)
    Alt-Left-arrow (contract-or-go-left)
    Alt-Up-arrow (goto-prev-visible) 
    Alt-Down-arrow (goto-next-visible)

Moving outline nodes
********************

When focus is in the outline::

    Shift-Down-arrow (move-outline-down) 
    Shift-Left-arrow (move-outline-left) 
    Shift-Right-arrow (move-outline-right) 
    Shift-Up-arrow (move-outline-up)

Regardless of focus::

    Alt-Shift-Down-arrow (move-outline-down) 
    Alt-Shift-Left-arrow (move-outline-left) 
    Alt-Shift-Right-arrow (move-outline-right) 
    Alt-Shift-Up-arrow (move-outline-up)
    Ctrl-D (move-outline-down)
    Ctrl-L (move-outline-left) 
    Ctrl-R (move-outline-right)
    Ctrl-U (move-outline-up)

Moving the cursor
*****************

When focus is in any of Leo's text panes (body pane, log pane, headlines):

    +-------------------+-----------------------+
    | **Key**           | **Move Cursor**       |
    +-------------------+-----------------------+
    | Arrow keys        | one character         |
    +-------------------+-----------------------+
    | Ctrl-LeftArrow    | back one word         |
    +-------------------+-----------------------+
    | Ctrl-RightArrow   | forward one word      |
    +-------------------+-----------------------+
    | Home              | beginning of line     |
    +-------------------+-----------------------+
    | End               | end of line           |
    +-------------------+-----------------------+
    | Ctrl-Home         | beginning of the body |
    +-------------------+-----------------------+
    | Ctrl-End          | end of body           |
    +-------------------+-----------------------+
    | PageDown          | down one page         |
    +-------------------+-----------------------+
    | PageUp            | up one page           |
    +-------------------+-----------------------+
    
Adding the Shift key modifier to any of the keys above moves the cursor and extends the selected text.

Executing minibuffer commands
+++++++++++++++++++++++++++++

Alt-X puts focus in the minibuffer. Ctrl-G escapes from the minibuffer.

Once there, you can use tab completion to reduce typing. For example, <Alt-X>open<tab> shows all commands that start with open.

Hit <Enter> to run a complete command.

Ctrl-P (repeat-complex-command) repeat the last command entered from the minibuffer.

Leo maintains a **command history list** of all minibuffer commands you have entered.

When focus is in the minibuffer, UpArrow shows the previous minibuffer command, and DnArrow show the commands before that.

The body text of an @data history-list *setting node* preloads commands into the command history list, ignoring lines starting with '#'. For example::

    run-pylint
    beautify-tree
    cff
    sort-lines
    # show-data
    check-clones
    expand-log-pane
    contract-log-pane

Frequently used commands
++++++++++++++++++++++++

For much more information, see the `Commands Reference <commands.html>`_.

Copy/Paste (text)::

    Ctrl-C (copy-text)
    Ctrl-K (kill)
    Ctrl-V (paste-text)
    Ctrl-X (cut-text)
    Ctrl-Y (yank)
    Alt-Y  (yank-pop)
    kill-...

Files::

    Ctrl-N (new) 
    Ctrl-O (open-outline)
    Ctrl-S (save-file) 
    Ctrl-Q (exit-leo)

Focus::

    Alt-T (focus-to-tree) 
    Ctrl-T (toggle-active-pane)
    Ctrl-Tab (tab-cycle-next)
    
Help::

    Alt-0 (vr-toggle)
    F1 (help) 
    F11 (help-for-command) 
    F12 (help-for-python)
    show-bindings
    show-settings
    help-for-...

Find/Replace::

    Ctrl-F (search-with-present-options) 
    Shift-Ctrl-R (replace-string)
    Ctrl-minus (replace-then-find) 
    F3 (find-next) 
    F2 (find-previous)
    
Minibuffer::

    Alt-X (full-command)
    Ctrl-G (keyboard-quit)
    Tab (not a command, completes typing)

Nodes::

    Ctrl-I or Insert (insert-node)
    Ctrl-H (edit-headline)
    <Return> (when editing a headline) (end-edit-headline)
    Ctrl-Shift-C (copy-node)
    Ctrl-Shift-X (cut-node) 
    Ctrl-Shift-V (paste-node) 
    Ctrl-{ (promote)
    Ctrl-} (demote)
    Ctrl-M (mark) 

Undo::

    Ctrl-Z (undo)
    Ctrl-Shift-Z (redo)

Gathering find commands
+++++++++++++++++++++++

The **clone find** commands, cfa and cff,  move clones of all nodes matching the search pattern under a single **organizer node**, created as the last top-level node. **Flattened** searches put all nodes as direct children of the organizer node::

    cfa     clone-find-all
    cff     clone-find-all-flattened
    
The **clone-marked** commands move clones of all marked nodes under an organizer node. Especially useful for gathering nodes by hand::

    cfam    clone-find-marked 
    cffm    clone-find-flattened-marked

Leo directives
++++++++++++++

Directives starting with '@ in the leftmost column
    
See the `Directives reference <directives.html>`_ for full details::

    @                       # starts doc part
    @c                      # ends doc part
    @color
    @doc                    # starts doc part
    @killcolor
    @nocolor
    @language python
    @language c
    @language rest          # restructured text
    @language plain         # plain text: no syntax coloring.
    @lineending lineending
    @nosearch               # suppress searching for cff & cfa commands.
    @pagewidth 100
    @tabwidth -4            # use spaces
    @tabwidth 8             # use tabs
    @nowrap
    @wrap
    
Leading whitespace is allowed (and significant) for::

    @all
    @others

Settings
++++++++

For documentation see node: "About this file" in leoSettings.leo::

    Command history:    @history-list
    Key bindings:       @shortcuts
    Visual settings:    @data qt-gui-plugin-style-sheet
    Enabling plugins:   @enabled-plugins

To disable a binding for a key, bind it to do-nothing::

    do-nothing = Insert
    
This overrides the following default binding in leoSettings.leo::

    insert-node = Insert

Node types
++++++++++

Supported by Leo's core::

    @chapter
    @rst, @rst-no-head, @rst-ignore, @rst-ignore-tree
    @settings
    @url

Within @settings trees::

    @bool, @buttons, @color, @commands
    @directory, @encoding
    @enabled-plugins, @float, @font,
    @history-list, @int
    @menus, @menu, @menuat, @item
    @openwith, @path, @shortcuts, @string

Supported by plugins::

    bookmarks.py:       @bookmarks, @bookmark
    at_folder.py:       @folder
    at_produce.py:      @produce
    at_view.py:         @clip, @strip, @view
    expfolder.py:       @expfolder
    mod_scripting.py:   @button, @command, @script
    viewrendered.py:    @graphics-script, @image
                        @html, @movie, @svg

Notable Plugins
+++++++++++++++

See the docstring of these plugins for more details::

    bookmarks.py:       Manages URL's used as bookmarks.
    contextmenu.py:     Creates context menus for headlines.
    demo.py:            Creates demos and slides.
    mod_scripting.py:   Supports @button and @command nodes.
    quicksearch.py:     Adds Nav tab for searching.
    todo.py:            To-do lists and simple project management.
    valuespace.py:      Creates an outline-oriented spreadsheet.
    viewrendered.py:    Creates a rendering pane.
                        Automatically loaded by Leo's help commands.
                        Supports @graphics-script, @image, @html,
                        @movie and @svg nodes.
    vim.py & xemacs.py  Interface with vim and xemacs.

External files (@<file> nodes)
++++++++++++++++++++++++++++++

.. From cheat sheet

\@<file> nodes create external files::

    @asis <filename>        write only, no sentinels, exact line endings
    @auto <filename>        recommended
    @clean <filename>       recommended
    @edit <filename>        @edit node contains entire file
    @file <filename>        recommended
    @nosent <filename>      write only, no sentinels
    
This table summarizes the differences between @<file> nodes::

                             Sections &   File data in
    @<file> kind  Sentinels?  @others?    .leo file?    Notes             
    ------------  ---------- -----------  ------------  -----
    @asis          no          no          yes
    @auto          no          yes         no           1, 2
    @auto-xx       no          yes         no           1, 2
    @clean         no          yes         yes     
    @edit          no          no          no    
    @file          yes         yes         no
    @nosent        no          yes         yes
    
\@auto nodes read files using language-specific importers.
By default, the file's extension determines the importer::

    Extensions                  Importer
    ----------                  --------
    .c, .cc, .c++, .cpp,.cxx    C
    .cs', .c#'                  C Sharp
    .el                         Elisp
    .h, .h++                    C
    .html, .htm                 HTML
    .ini                        Config file
    .ipynb                      Jupyter notebook
    .java                       Java
    .js                         JavaScript
    .md                         Markdown
    .org                        Org Mode
    .otl                        Vim outline
    .pas                        Pascal
    .php                        PHP
    .py, .pyi, .pyw             Python
    .rest, .rst                 reStructuredText
    .ts                         TypeScript
    .xml                        XML
    
You can also specify importers *explicitly* as follows::

    @auto-xxx           Importer
    ---------           --------
    @auto-ctext         ctext
    @auto-markdown      markdown
    @auto-md            markdown
    @auto-org           org-mode
    @auto-org-mode      org-mode
    @auto-otl           vimoutline
    @auto-vim-outline   vimoutline
    @auto-rst           reStructuredText
    
**Important**: The importers/exporters for markdown, org-mode, reStructuredText and vimoutline files automatically generate section headings corresponding to Leo's outline level. Body text of the top-level @auto node is ignored.
    
See the `Directives reference <directives.html>`_ for full details.

Sections
++++++++

**Section names** have the form::

    << any text, except double closing angle brackets >>
    
**Section-definition nodes** have headlines starting with a section name.

Leo performs **expansions** for all @<file> nodes except @asis.

Expansion of @all:

- Leo replaces @all by the *unexpanded* body text of *all* nodes.

Expansion of section names and @others:

- Leo replaces section names in body text by the *expanded*
  text of the corresponding section definition node.
  
- Leo replaces @others with the *expanded* text of all nodes
  that *aren't* section-definition nodes.

Scripting
+++++++++

This section lists the ivars (instance variables), properties, functions and methods most commonly used in Leo scripts.

**Very important**: use Alt-1 (toggle-autocompleter) and Alt-2 (toggle-calltips) to recreate these lists as you type.

Pre-defined symbols
*******************

execute-script predefines::

    c: The commander of the present outline.
    g: The leo.core.leoGlobals module.
    p: The presently selected position, c.p.

LeoApp class
************

**Ivars**::

    g.app                   A LeoApp instance.
    g.app.gui               A LeoGui instance. 
    g.app.pluginsController A LeoPluginsController instance.
    g.app.*                 Leo's global variables.

Commands class
**************

**Ivars**::

    c.config                c's configuration object
    c.frame                 c's outer frame, a leoFrame instance.
    c.undoer                c's undo handler.
    c.user_dict             A temporary dict for use of scripts and plugins.
    
**SubCommanders**::

    # In leo/core...
    c.atFileCommands
    c.chapterController
    c.fileCommands
    c.findCommands
    c.importCommands
    c.keyHandler = c.k
    c.persistenceController
    c.printingController
    c.rstCommands
    c.shadowController
    c.tangleCommands
    c.testManager
    c.vimCommands

    # In leo/commands...
    c.abbrevCommands
    c.controlCommands
    c.convertCommands
    c.debugCommands
    c.editCommands
    c.editFileCommands
    c.gotoCommands
    c.helpCommands
    c.keyHandlerCommands
    c.killBufferCommands
    c.rectangleCommands
    c.spellCommands
    
**Generators** (New in Leo 5.5: All generators yield distinct positions)::

    c.all_positions()
    c.all_unique_positions()
    
**Most useful methods**::

    c.isChanged()
    c.deletePositionsInList(aList, callback=None)
                            # safely deletes all the positions in aList.
    c.positionExists(p)
    c.redraw(p=None)        # Redraw the screen. Select p if given.
    c.save()                # Save the present outline.
    c.selectPosition()
    
**Official ivars** of any leoFrame f::

    f.c                     is the frame’s commander.
    f.body                  is a leoBody instance.
    f.body.bodyCtl          is a leoQTextEditWidget instance.
    f.body.bodyCtrl.widget  is a LeoQTextBrowser(QTextBrowser) instance.
    f.log                   is a leoLog instance.
    f.tree                  is a leoQtTree instance.
    f.tree.treeWidget       is a LeoQTreeWidget (a QTreeWidget) instance.
    
Use autocompletion to explore these objects!

Undoing commands
****************

If you want to make a command undoable, you must create "before" and "after" snapshots of the parts of the outline that may change. Here are some examples.  Leo's source code contains many other examples.

Undoably changing body text
^^^^^^^^^^^^^^^^^^^^^^^^^^^

To undo a single change to body text::

    command = 'my-command-name'
    b = c.undoer.beforeChangeNodeContents(p, oldYScroll=ypos)
    # Change p's body text.
    c.undoer.afterChangeNodeContents(p,
        command=command, bunch=b, dirtyVnodeList=[])

Undoably changing multiple nodes
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If your command changes multiple nodes, the pattern is::

    u, undoType = c.undoer, 'command-name'
    u.beforeChangeGroup(c.p, undoType)
    dirtyVnodeList = []
    changed = False
    # For each change, do something like the following:
    for p in to_be_changed_nodes:
        # Change p.
        dirtyVnodeList.append(p.v)
        u.afterChangeNodeContents(p, undoType, bunch)
        changed = True
    if changed:
        u.afterChangeGroup(c.p, undoType,
            reportFlag=False,
            dirtyVnodeList=dirtyVnodeList)

VNode class
***********

**Ivars**::

    v.b:    v's body text.
    v.gnx   v's gnx.
    v.h:    v's headline text.
    v.u:    v.unknownAttributes, a persistent Python dictionary.
    
v.u (uA's or unknownAttributes or userAttributes) allow plugins or scripts
to associate persistent data with vnodes. For details see the section about
`userAttributes <customizing.html#adding-extensible-attributes-to-nodes-and-leo-files>`_ in the `Customizing Leo <customizing.html>`_ chapter.

*Important*: Generally speaking, vnode properties are fast, while the
corresponding position properties are much slower. Nevertheless, scripts
should usually use *position* properties rather than *vnode* properties
because the position properties handle recoloring and other details.
Scripts should use *vnode* properties only when making batch changes to
vnodes.

Position class
**************

**Properties**::

    p.b: same as p.v.b.  *Warning*: p.b = s is expensive.
    p.h: same as p.v.h.  *Warning*: p.h = s is expensive.
    p.u: same as p.v.u.
    
**Generators** (New in Leo 5.5: All generators yield distinct positions)::

    p.children()
    p.parents()
    p.self_and_parents()
    p.self_and_siblings()
    p.following_siblings()
    p.subtree()
    p.self_and_subtree()

**Getters** These return *new positions*::

    p.back()
    p.children()
    p.copy()
    p.firstChild()
    p.hasBack()
    p.hasChildren()
    p.hasNext()
    p.hasParent()
    p.hasThreadBack()
    p.hasThreadNext()
    p.isAncestorOf(p2)
    p.isAnyAtFileNode()
    p.isAt...Node()
    p.isCloned()
    p.isDirty()
    p.isExpanded()
    p.isMarked()
    p.isRoot()
    p.isVisible()
    p.lastChild()
    p.level()
    p.next()
    p.nodeAfterTree()
    p.nthChild()
    p.numberOfChildren()
    p.parent()
    p.parents()
    p.threadBack()
    p.threadNext()
    p.visBack()
    p.visNext()
    
**Setters**::

    p.setDirty()  *Warning*: p.setDirty() is expensive.
    p.setMarked()

**Operations on nodes**::

    p.clone()
    p.contract()
    p.doDelete(new_position)
    p.expand()
    p.insertAfter()
    p.insertAsNthChild(n)
    p.insertBefore()
    p.moveAfter(p2)
    p.moveToFirstChildOf(parent,n)
    p.moveToLastChildOf(parent,n)
    p.moveToNthChildOf(parent,n)
    p.moveToRoot(oldRoot=None)
        # oldRoot **must** be the old root position if it exists.
        
**Moving positions**

The following move positions *themselves*: they change the node to which a
position refers. They do *not* change outline structure in any way! Use
these when generators are not flexible enough::

    p.moveToBack()
    p.moveToFirstChild()
    p.moveToLastChild()
    p.moveToLastNode()
    p.moveToNext()
    p.moveToNodeAfterTree(p2)
    p.moveToNthChild(n)) 
    p.moveToParent()
    p.moveToThreadBack()
    p.moveToThreadNext()
    p.moveToVisBack(c)
    p.moveToVisNext(c)

leo.core.leoGlobals module
**************************

For full details, see @file leoGlobals.py in LeoPyRef.leo.

**g vars**::

    g.app
    g.app.gui
    g.app.windowlist
    g.unitTesting
    g.user_dict  # a temporary dict for use of scripts and plugins.
    
**g decorator**::

    @g.command(command-name)
    
**g functions** (the most interesting: there are many more in leoGlobals.py)::
    
    g.angleBrackets()
    g.app.commanders()
    g.app.gui.guiName()
    g.es(*args,**keys)
    g.es_print(*args,**keys)
    g.es_exception()
    g.getScript(c,p,
        useSelectedText=True,
        forcePythonSentinels=True,
        useSentinels=True)
    g.openWithFileName(fileName,old_c=None,gui=None)
    g.os_path_... # Wrappers for os.path methods.
    g.pdb(message='')
    g.toEncodedString(s,encoding='utf-8',reportErrors=False)
    g.toUnicode(s, encoding='utf-8',reportErrors=False)
    g.trace(*args,**keys)
    g.warning(*args,**keys)

Test driven development
***********************

- Use `imp.reload <https://docs.python.org/3/library/imp.html>`_ to reload all changed modules.
- Make sure to *instantiate* any changed objects.
- See `this section <unitTesting.html#test-driven-development-in-leo>`_ for full details.

Performance gotchas
*******************

**Warning**: The p.b and p.h setters and p.setDirty() are *very* expensive:

- p.b = s calls c.setBodyString(p, s) which will recolor body text and update the node's icon.
- p.h = s calls c.setHeadString(p, s) which calls p.setDirty().
- p.setDirty() changes the icons of all ancestor @file nodes.

In contrast, the corresponding p.v.b and p.v.b setters and p.v.setDirty() are extremely fast.

Usually, code *should* use the p.b and p.h setters and p.setDirty(), despite their cost, because they update Leo's outline pane properly. Calling c.redraw() is *not* enough.

These performance gotchas become important for repetitive commands, like cff, replace-all and recursive import. In such situations, code should use p.v.b and p.v.h setters instead of p.b and p.h setters.

Prompting for command arguments
*******************************

Example 1: Prompt for one arg
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

::

    @g.command('i1')
    def i1_command(event):
        c = event.get('c')
        if not c: return
            
        def callback(args, c, event):
            g.trace(args)
            c.bodyWantsFocus()
    
        c.interactive(callback, event, prompts=['Prompt: '])

Example 2: Prompt for 2 args
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

::

    @g.command('i2')
    def i2_command(event):
        c = event.get('c')
        if not c: return
            
        def callback(args, c, event):
            g.trace(args)
            c.bodyWantsFocus()
    
        c.interactive(callback, event,
            prompts=['Find: ', ' Replace: '])

Example 3: Prompt for 3 args
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

::

    @g.command('i3')
    def i3_command(event):
        c = event.get('c')
        if not c: return
            
        def callback(args, c, event):
            g.trace(args)
            c.bodyWantsFocus()
    
        c.interactive(callback, event,
            prompts=['One: ', ' Two: ', ' Three: '])

Naming conventions in Leo's core
********************************

LeoPyRef.leo contains all of Leo's core source code.

Leo's code uses the following conventions throughout:

c:  a commander.
ch: a character.
d:  a dialog or a dict.
f:  an open file.
fn: a file name.
g:  the leoGlobals module.
i, j, k: indices into a string.
p:  a Position.
s:  a string.
t:  a text widget.
u:  an undoer.
w:  a gui widget.
v:  a Vnode
z:  a local temp.

In more limited contexts, the following conventions apply:

si:     a g.ShortcutInfo object.
ks:     a g.KeyStroke object
stroke: a KeyStroke object.

btw:    leoFrame.BaseTextWrapper
stw:    leoFrame.StringTextWrapper

bqtw:   qt_text.BaseQTextWrapper
lqtb:   qt_text.LeoQTextBrowser
qhlw:   qt_text.QHeadlineWrapper
qmbw:   qt_text.QMinibufferWrapper
qlew:   qt_text.QLineEditWrapper
qsciw:  qt_text.QScintiallaWrapper
qtew:   qt_text.QTextEditWrapper

Names defined in Leo's core are unlikely to change, especially names used outside their defining module. This includes virtually everything in leoGlobals.py, and many names in leoCommands.py and other files.

Official ivars
^^^^^^^^^^^^^^

The following 'official' ivars (instance vars) will always exist:

c.frame                 The frame containing the log,body,tree, etc.
c.frame.body            The body pane.
c.frame.body.widget     The gui widget for the body pane.
c.frame.body.wrapper    The high level interface for the body widget.
c.frame.iconBar         The icon bar.
c.frame.log             The log pane.
c.frame.log.widget      The gui widget for the log pane.
c.frame.log.wrapper     The high-level interface for the log pane.
c.frame.tree            The tree pane.

The following were official ivars that no longer exist:

c.frame.body.bodyCtrl   Use c.frame.body.wrapper instead.
c.frame.log.logCtrl     Use c.frame.log.wrapper instead.

Widgets and wrappers
********************

A **widget** is an actual Qt widget. Leo's core seldom accesses widgets directly.  Instead, a  **wrapper class** defines a standard api that hides the details of the underlying gui **text** widgets.

Leo's core uses the wrapper api almost exclusively. That is, Leo's core code treats wrappers *as if* they were only text widgets there are!

A back door exists for special cases. All wrapper classes define an official ``widget`` ivar, so core or plugin code can gain access to the real Qt widget using wrapper.widget. Searching for wrapper.widget will find all gui-dependent snippets of code in Leo's core.

Command-line options
++++++++++++++++++++

::

    Usage: launchLeo.py [options] file1, file2, ...
    
    Options:
      -h, --help            show this help message and exit
      --debug               enable debug mode
      --diff                use Leo as an external git diff
      --fullscreen          start fullscreen
      --ipython             enable ipython support
      --fail-fast           stop unit tests after the first failure
      --gui=GUI             gui to use (qt/qttabs)
      --load-type=LOAD_TYPE
                            @<file> type for loading non-outlines from command
                            line
      --maximized           start maximized
      --minimized           start minimized
      --no-cache            disable reading of cached files
      --no-plugins          disable all plugins
      --no-splash           disable the splash screen
      --screen-shot=SCREENSHOT_FN
                            take a screen shot and then exit
      --script=SCRIPT       execute a script and then exit
      --script-window=SCRIPT_WINDOW
                            open a window for scripts
      --select=SELECT       headline or gnx of node to select
      --silent              disable all log messages
      --trace-plugins       trace imports of plugins
      -v, --version         print version number and exit
      --window-size=WINDOW_SIZE
                            initial window size (height x width)

Learning to be a Leo developer
++++++++++++++++++++++++++++++

Code academy
************

Leo's Code Academy posts discuss how to do useful things in Leo. The following are distilled from online discussions about Leo's scripting.

CA: uA's
^^^^^^^^

uA's (user Attributes) associate arbitrary data with any vnode. uA's are dictionaries of dictionaries--an **outer dictionary** and zero or more **inner dictionaries**. The outer dictionary associates plugin names (or Leo's core) with inner dictionaries. The inner dictionaries carry the actual data.

The v.u or p.v properties get and set uA's. You can think of p.u as a synonym for p.v.unknownAttributes on both sides of an assignment. For example::

    plugin_name = 'test_plugin'
    d = p.u.get(plugin_name,{})
    d ['n'] = 8
    p.u [plugin_name] = d

p.u is the outer dictionary. p.u.get.(plugin_name, {}) is the inner dictionary. The last line is all that is needed to update the outer dictionary!

It is easy to search for particular uA's. The following script prints all the keys in the outer-level uA dictionaries:

    for p in c.all_unique_positions():
        if p.u:
            print(p.h, sorted(p.u.keys()))

This is a typical usage of Leo's generators.  Generators visit each position (or node) quickly. Even if you aren't going to program much, you should be aware of how easy it is to get and set the data in each node. In fact, now would be a great time to read Leo's Scripting Tutorial again :-) This will allow you to "dream bigger" with Leo.

The following script creates a list of all positions having an icon, that is, an outer uA dict with a 'icon' key.

    aList = [p.copy() for p in c.all_unique_positions() if 'icon' in p.u]
    print('\n'.join([p.h for p in aList]))

*Important*: If you don't understand these lines, please study Python's list comprehensions.  They are incredibly useful. '\n'.join(aList) is a great idiom to know.  str.join is one of python's most useful string methods. It converts between lists and strings.

CA: icons
^^^^^^^^^

This script inserts three icons in the current outline node. Running
the script again will insert three more::

    table = (
        'edittrash.png',
        'connect_no.png',
        'error.png',
    )
    for icon in table:
        fn = g.os_path_finalize_join(g.app.loadDir,
            '..', 'Icons', 'Tango', '16x16', 'status', icon)
        if g.os_path_exists(fn):
            c.editCommands.insertIconFromFile(path=fn)

This deletes all icons of the node at position p::

    c.editCommands.deleteNodeIcons(p=p)

CA: using git
^^^^^^^^^^^^^

Using Leo’s latest sources from GitHub is highly recommended. Once git is installed, the following gets the latest Leo sources::

    git clone https://github.com/leo-editor/leo-editor.git

Thereafter, you can update Leo's sources with::

    git pull

Git is great in tracking history and reverting unwanted changes. And it has many other benefits.

Using git is very similar to using bzr or hg or any other SCCS.  To change Leo, you add files, you commit files, and you push files.  That's about it.

CA: finding nodes with c.cloneFindByPredicate
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

c.cloneFindByPredicate is a powerful new addition to Leo.  Here is its docstring::

    Traverse the tree given using the generator, cloning all positions for
    which predicate(p) is True. Undoably move all clones to a new node, created
    as the last top-level node. Returns the newly-created node. Arguments:

    generator,      The generator used to traverse the tree.
    predicate,      A function of one argument p returning true if 
                    p should be included.
    failMsg=None,   Message given if nothing found. Default is no message.
    flatten=False,  True: Move all node to be parents of the root node.
    iconPath=None,  Full path to icon to attach to all matches.
    redraw=True,    True: redraw the screen.
    undo_type=None, The undo/redo name shown in the Edit:Undo menu.
                    The default is 'clone-find-predicate'
                    
For example, clone-find-all-marked command is essentially::
    
    @cmd('clone-find-all-marked')
    def cloneFindMarked(self, flatten):
        
        def isMarked(p):
            return p.isMarked()
            
        self.cloneFindByPredicate(
            generator = self.all_unique_positions,
            predicate = isMarked,
            failMsg = 'nothing found',
            flatten = flatten,
            undoType = 'clone-find-marked',
        )
        
The predicate could filter on an attribute or *combination* of attributes. For example, the predicate could return p has attributes A and B but *not* attribute C. This instantly gives Leo full database query capabilities. If we then hoist the resulting node we see *all and only* those nodes satisfying the query.

These following position methods make it easy to skip @ignore trees or @<file> trees containing @all::
        
    p.is_at_all()          True if p is an @<file> node containing an @all directive.
    p.in_at_all()          True if p is in an @<file> tree whose root contains @all.
    p.is_at_ignore()       True if p is an @ignore node
    p.in_at_ignore_tree()  True if p is in an @ignore tree.

For example, here is how to gather only those marked nodes that lie outside any @ignore tree::

    def isMarked(p):
        return p.isMarked() and not p.in_at_ignore_tree()
      
    c.cloneFindByPredicate(
        generator = self.all_unique_positions,
        predicate = isMarked,
        flatten = flatten,
        undoType = 'gather-marked',
    )

Leo University
**************

Leo University is a project devoted to help people become Leo developers.

Here is the main page.  It contains links to individual lessons.
https://github.com/leo-editor/leo-editor/issues/816

Architecture
************

Leo uses a model/view/controller architecture.

- Controller: The Commands class and its helpers in leoCommands.py and leoEditCommands.py.

- Model: The VNode and Position classes in leoNodes.py.

- View: The gui-independent base classes are in the node "Gui Base Classes". The Qt-Specific subclasses are in the node "Qt gui".

**Important**: The general organization of these classes have changed hardly at all in Leo's 20+ year history.  The reason is that what each class does is fairly obvious.  How the gets the job done may have changed drastically, but *that's an internal implementation detail of the class itself*.  This is the crucial design principle that allows Leo's code to remain stable.  *Classes do not know or meddle in the internal details of other classes*.  As a result, nobody, including EKR, needs to remember internal details.

