"tkinter.ttk" --- Tk主题小部件
******************************

**源代码:** Lib/tkinter/ttk.py

======================================================================

The "tkinter.ttk" module provides access to the Tk themed widget set,
introduced in Tk 8.5. If Python has not been compiled against Tk 8.5,
this module can still be accessed if *Tile* has been installed.  The
former method using Tk 8.5 provides additional benefits including
anti-aliased font rendering under X11 and window transparency
(requiring a composition window manager on X11).

The basic idea for "tkinter.ttk" is to separate, to the extent
possible, the code implementing a widget's behavior from the code
implementing its appearance.

也參考:

  Tk Widget Styling Support
     A document introducing theming support for Tk


使用 Ttk
========

To start using Ttk, import its module:

   from tkinter import ttk

To override the basic Tk widgets, the import should follow the Tk
import:

   from tkinter import *
   from tkinter.ttk import *

That code causes several "tkinter.ttk" widgets ("Button",
"Checkbutton", "Entry", "Frame", "Label", "LabelFrame", "Menubutton",
"PanedWindow", "Radiobutton", "Scale" and "Scrollbar") to
automatically replace the Tk widgets.

This has the direct benefit of using the new widgets which gives a
better look and feel across platforms; however, the replacement
widgets are not completely compatible. The main difference is that
widget options such as "fg", "bg" and others related to widget styling
are no longer present in Ttk widgets.  Instead, use  the "ttk.Style"
class for improved styling effects.

也參考:

  Converting existing applications to use Tile widgets
     A monograph (using Tcl terminology) about differences typically
     encountered when moving applications to use the new widgets.


Ttk Widgets
===========

Ttk comes with 18 widgets, twelve of which already existed in tkinter:
"Button", "Checkbutton", "Entry", "Frame", "Label", "LabelFrame",
"Menubutton", "PanedWindow", "Radiobutton", "Scale", "Scrollbar", and
"Spinbox". The other six are new: "Combobox", "Notebook",
"Progressbar", "Separator", "Sizegrip" and "Treeview". And all them
are subclasses of "Widget".

Using the Ttk widgets gives the application an improved look and feel.
As discussed above, there are differences in how the styling is coded.

Tk 代码:

   l1 = tkinter.Label(text="Test", fg="black", bg="white")
   l2 = tkinter.Label(text="Test", fg="black", bg="white")

Ttk 代码:

   style = ttk.Style()
   style.configure("BW.TLabel", foreground="black", background="white")

   l1 = ttk.Label(text="Test", style="BW.TLabel")
   l2 = ttk.Label(text="Test", style="BW.TLabel")

有关 TtkStyling 的更多信息，请参阅 "Style" 类文档。


Widget
======

"ttk.Widget" 定义了 Tk 主题小部件支持的标准选项和方法，不应该直接实例
化。


标准选项
--------

所有 "ttk" 小部件接受以下选项：

   +-------------+----------------------------------------------------------------+
   | 选项        | 描述                                                           |
   |=============|================================================================|
   | 类          | 指定窗口类。在查询选项数据库中窗口的其他选项时，使用该类，确定 |
   |             | 窗口 的默认绑定标签，以及选择窗口小部件的默认布局和样式。此选  |
   |             | 项仅为只读 ，并且只能在创建窗口时指定。                        |
   +-------------+----------------------------------------------------------------+
   | cursor      | 指定要用于窗口小部件的鼠标光标。如果设置为空字符串（默认值）， |
   |             | 则为 父窗口小部件继承光标.                                     |
   +-------------+----------------------------------------------------------------+
   | takefocus   | 确定窗口是否在键盘遍历期间接受焦点。返回0或1，返回空字符串。如 |
   |             | 果返 回0，则表示在键盘遍历期间应该跳过该窗口。如果为1，则表示  |
   |             | 只要可以查 看窗口就应该接收输入焦点。并且空字符串意味着遍历脚  |
   |             | 本决定是否关注窗 口。                                          |
   +-------------+----------------------------------------------------------------+
   | style       | 可用于指定自定义窗口小部件样式。                               |
   +-------------+----------------------------------------------------------------+


Scrollable Widget Options
-------------------------

The following options are supported by widgets that are controlled by
a scrollbar.

   +------------------+-----------------------------------------------------------+
   | 选项             | 描述                                                      |
   |==================|===========================================================|
   | xscrollcommand   | Used to communicate with horizontal scrollbars.  When the |
   |                  | view in the widget's window change, the widget will       |
   |                  | generate a Tcl command based on the scrollcommand.        |
   |                  | Usually this option consists of the method                |
   |                  | "Scrollbar.set()" of some scrollbar. This will cause the  |
   |                  | scrollbar to be updated whenever the view in the window   |
   |                  | changes.                                                  |
   +------------------+-----------------------------------------------------------+
   | yscrollcommand   | Used to communicate with vertical scrollbars. For some    |
   |                  | more information, see above.                              |
   +------------------+-----------------------------------------------------------+


Label Options
-------------

The following options are supported by labels, buttons and other
button-like widgets.

   +----------------+-------------------------------------------------------------+
   | 选项           | 描述                                                        |
   |================|=============================================================|
   | text           | Specifies a text string to be displayed inside the widget.  |
   +----------------+-------------------------------------------------------------+
   | textvariable   | Specifies a name whose value will be used in place of the   |
   |                | text option resource.                                       |
   +----------------+-------------------------------------------------------------+
   | underline      | If set, specifies the index (0-based) of a character to     |
   |                | underline in the text string. The underline character is    |
   |                | used for mnemonic activation.                               |
   +----------------+-------------------------------------------------------------+
   | image          | Specifies an image to display. This is a list of 1 or more  |
   |                | elements. The first element is the default image name. The  |
   |                | rest of the list if a sequence of statespec/value pairs as  |
   |                | defined by "Style.map()", specifying different images to    |
   |                | use when the widget is in a particular state or a           |
   |                | combination of states. All images in the list should have   |
   |                | the same size.                                              |
   +----------------+-------------------------------------------------------------+
   | compound       | Specifies how to display the image relative to the text, in |
   |                | the case both text and images options are present. Valid    |
   |                | values are:  * text: display text only  * image: display    |
   |                | image only  * top, bottom, left, right: display image       |
   |                | above, below, left of, or right of the text, respectively.  |
   |                | * none: the default. display the image if present,          |
   |                | otherwise the text.                                         |
   +----------------+-------------------------------------------------------------+
   | width          | If greater than zero, specifies how much space, in          |
   |                | character widths, to allocate for the text label, if less   |
   |                | than zero, specifies a minimum width. If zero or            |
   |                | unspecified, the natural width of the text label is used.   |
   +----------------+-------------------------------------------------------------+


Compatibility Options
---------------------

   +----------+------------------------------------------------------------------+
   | 选项     | 描述                                                             |
   |==========|==================================================================|
   | state    | May be set to "normal" or "disabled" to control the "disabled"   |
   |          | state bit. This is a write-only option: setting it changes the   |
   |          | widget state, but the "Widget.state()" method does not affect    |
   |          | this option.                                                     |
   +----------+------------------------------------------------------------------+


Widget States
-------------

The widget state is a bitmap of independent state flags.

   +--------------+---------------------------------------------------------------+
   | 标志         | 描述                                                          |
   |==============|===============================================================|
   | active       | The mouse cursor is over the widget and pressing a mouse      |
   |              | button will cause some action to occur                        |
   +--------------+---------------------------------------------------------------+
   | disabled     | Widget is disabled under program control                      |
   +--------------+---------------------------------------------------------------+
   | focus        | Widget has keyboard focus                                     |
   +--------------+---------------------------------------------------------------+
   | pressed      | Widget is being pressed                                       |
   +--------------+---------------------------------------------------------------+
   | selected     | "On", "true", or "current" for things like Checkbuttons and   |
   |              | radiobuttons                                                  |
   +--------------+---------------------------------------------------------------+
   | background   | Windows and Mac have a notion of an "active" or foreground    |
   |              | window. The *background* state is set for widgets in a        |
   |              | background window, and cleared for those in the foreground    |
   |              | window                                                        |
   +--------------+---------------------------------------------------------------+
   | 只读         | Widget should not allow user modification                     |
   +--------------+---------------------------------------------------------------+
   | alternate    | A widget-specific alternate display format                    |
   +--------------+---------------------------------------------------------------+
   | invalid      | The widget's value is invalid                                 |
   +--------------+---------------------------------------------------------------+

A state specification is a sequence of state names, optionally
prefixed with an exclamation point indicating that the bit is off.


ttk.Widget
----------

Besides the methods described below, the "ttk.Widget" supports the
methods "tkinter.Widget.cget()" and "tkinter.Widget.configure()".

class tkinter.ttk.Widget

   identify(x, y)

      Returns the name of the element at position *x* *y*, or the
      empty string if the point does not lie within any element.

      *x* and *y* are pixel coordinates relative to the widget.

   instate(statespec, callback=None, *args, **kw)

      Test the widget's state. If a callback is not specified, returns
      "True" if the widget state matches *statespec* and "False"
      otherwise. If callback is specified then it is called with args
      if widget state matches *statespec*.

   state(statespec=None)

      Modify or inquire widget state. If *statespec* is specified,
      sets the widget state according to it and return a new
      *statespec* indicating which flags were changed. If *statespec*
      is not specified, returns the currently-enabled state flags.

   *statespec* will usually be a list or a tuple.


Combobox
========

The "ttk.Combobox" widget combines a text field with a pop-down list
of values. This widget is a subclass of "Entry".

Besides the methods inherited from "Widget": "Widget.cget()",
"Widget.configure()", "Widget.identify()", "Widget.instate()" and
"Widget.state()", and the following inherited from "Entry":
"Entry.bbox()", "Entry.delete()", "Entry.icursor()", "Entry.index()",
"Entry.insert()", "Entry.selection()", "Entry.xview()", it has some
other methods, described at "ttk.Combobox".


选项
----

This widget accepts the following specific options:

   +-------------------+----------------------------------------------------------+
   | 选项              | 描述                                                     |
   |===================|==========================================================|
   | exportselection   | Boolean value. If set, the widget selection is linked to |
   |                   | the Window Manager selection (which can be returned by   |
   |                   | invoking Misc.selection_get, for example).               |
   +-------------------+----------------------------------------------------------+
   | justify           | Specifies how the text is aligned within the widget. One |
   |                   | of "left", "center", or "right".                         |
   +-------------------+----------------------------------------------------------+
   | height            | Specifies the height of the pop-down listbox, in rows.   |
   +-------------------+----------------------------------------------------------+
   | postcommand       | A script (possibly registered with Misc.register) that   |
   |                   | is called immediately before displaying the values. It   |
   |                   | may specify which values to display.                     |
   +-------------------+----------------------------------------------------------+
   | state             | One of "normal", "readonly", or "disabled". In the       |
   |                   | "readonly" state, the value may not be edited directly,  |
   |                   | and the user can only selection of the values from the   |
   |                   | dropdown list. In the "normal" state, the text field is  |
   |                   | directly editable. In the "disabled" state, no           |
   |                   | interaction is possible.                                 |
   +-------------------+----------------------------------------------------------+
   | textvariable      | Specifies a name whose value is linked to the widget     |
   |                   | value. Whenever the value associated with that name      |
   |                   | changes, the widget value is updated, and vice versa.    |
   |                   | See "tkinter.StringVar".                                 |
   +-------------------+----------------------------------------------------------+
   | values            | Specifies the list of values to display in the drop-down |
   |                   | listbox.                                                 |
   +-------------------+----------------------------------------------------------+
   | width             | Specifies an integer value indicating the desired width  |
   |                   | of the entry window, in average-size characters of the   |
   |                   | widget's font.                                           |
   +-------------------+----------------------------------------------------------+


Virtual events
--------------

The combobox widgets generates a **<<ComboboxSelected>>** virtual
event when the user selects an element from the list of values.


ttk.Combobox
------------

class tkinter.ttk.Combobox

   current(newindex=None)

      If *newindex* is specified, sets the combobox value to the
      element position *newindex*. Otherwise, returns the index of the
      current value or -1 if the current value is not in the values
      list.

   get()

      Returns the current value of the combobox.

   set(value)

      Sets the value of the combobox to *value*.


Spinbox
=======

The "ttk.Spinbox" widget is a "ttk.Entry" enhanced with increment and
decrement arrows.  It can be used for numbers or lists of string
values. This widget is a subclass of "Entry".

Besides the methods inherited from "Widget": "Widget.cget()",
"Widget.configure()", "Widget.identify()", "Widget.instate()" and
"Widget.state()", and the following inherited from "Entry":
"Entry.bbox()", "Entry.delete()", "Entry.icursor()", "Entry.index()",
"Entry.insert()", "Entry.xview()", it has some other methods,
described at "ttk.Spinbox".


选项
----

This widget accepts the following specific options:

+------------------------+--------------------------------------------------------+
| 选项                   | 描述                                                   |
|========================|========================================================|
| from                   | Float value.  If set, this is the minimum value to     |
|                        | which the decrement button will decrement.  Must be    |
|                        | spelled as "from_" when used as an argument, since     |
|                        | "from" is a Python keyword.                            |
+------------------------+--------------------------------------------------------+
| to                     | Float value.  If set, this is the maximum value to     |
|                        | which the increment button will increment.             |
+------------------------+--------------------------------------------------------+
| increment              | Float value.  Specifies the amount which the           |
|                        | increment/decrement buttons change the value. Defaults |
|                        | to 1.0.                                                |
+------------------------+--------------------------------------------------------+
| values                 | Sequence of string or float values.  If specified, the |
|                        | increment/decrement buttons will cycle through the     |
|                        | items in this sequence rather than incrementing or     |
|                        | decrementing numbers.                                  |
+------------------------+--------------------------------------------------------+
| wrap                   | Boolean value.  If "True", increment and decrement     |
|                        | buttons will cycle from the "to" value to the "from"   |
|                        | value or the "from" value to the "to" value,           |
|                        | respectively.                                          |
+------------------------+--------------------------------------------------------+
| 格式                   | String value.  This specifies the format of numbers    |
|                        | set by the increment/decrement buttons.  It must be in |
|                        | the form "%W.Pf", where W is the padded width of the   |
|                        | value, P is the precision, and '%' and 'f' are         |
|                        | literal.                                               |
+------------------------+--------------------------------------------------------+
| command                | Python callable.  Will be called with no arguments     |
|                        | whenever either of the increment or decrement buttons  |
|                        | are pressed.                                           |
+------------------------+--------------------------------------------------------+


Virtual events
--------------

The spinbox widget generates an **<<Increment>>** virtual event when
the user presses <Up>, and a **<<Decrement>>** virtual event when the
user presses <Down>.


ttk.Spinbox
-----------

class tkinter.ttk.Spinbox

   get()

      Returns the current value of the spinbox.

   set(value)

      Sets the value of the spinbox to *value*.


Notebook
========

Ttk Notebook widget manages a collection of windows and displays a
single one at a time. Each child window is associated with a tab,
which the user may select to change the currently-displayed window.


选项
----

This widget accepts the following specific options:

   +-----------+------------------------------------------------------------------+
   | 选项      | 描述                                                             |
   |===========|==================================================================|
   | height    | If present and greater than zero, specifies the desired height   |
   |           | of the pane area (not including internal padding or tabs).       |
   |           | Otherwise, the maximum height of all panes is used.              |
   +-----------+------------------------------------------------------------------+
   | padding   | Specifies the amount of extra space to add around the outside of |
   |           | the notebook. The padding is a list up to four length            |
   |           | specifications left top right bottom. If fewer than four         |
   |           | elements are specified, bottom defaults to top, right defaults   |
   |           | to left, and top defaults to left.                               |
   +-----------+------------------------------------------------------------------+
   | width     | If present and greater than zero, specified the desired width of |
   |           | the pane area (not including internal padding). Otherwise, the   |
   |           | maximum width of all panes is used.                              |
   +-----------+------------------------------------------------------------------+


Tab Options
-----------

There are also specific options for tabs:

   +-------------+----------------------------------------------------------------+
   | 选项        | 描述                                                           |
   |=============|================================================================|
   | state       | Either "normal", "disabled" or "hidden". If "disabled", then   |
   |             | the tab is not selectable. If "hidden", then the tab is not    |
   |             | shown.                                                         |
   +-------------+----------------------------------------------------------------+
   | sticky      | Specifies how the child window is positioned within the pane   |
   |             | area. Value is a string containing zero or more of the         |
   |             | characters "n", "s", "e" or "w". Each letter refers to a side  |
   |             | (north, south, east or west) that the child window will stick  |
   |             | to, as per the "grid()" geometry manager.                      |
   +-------------+----------------------------------------------------------------+
   | padding     | Specifies the amount of extra space to add between the         |
   |             | notebook and this pane. Syntax is the same as for the option   |
   |             | padding used by this widget.                                   |
   +-------------+----------------------------------------------------------------+
   | text        | Specifies a text to be displayed in the tab.                   |
   +-------------+----------------------------------------------------------------+
   | image       | Specifies an image to display in the tab. See the option image |
   |             | described in "Widget".                                         |
   +-------------+----------------------------------------------------------------+
   | compound    | Specifies how to display the image relative to the text, in    |
   |             | the case both options text and image are present. See Label    |
   |             | Options for legal values.                                      |
   +-------------+----------------------------------------------------------------+
   | underline   | Specifies the index (0-based) of a character to underline in   |
   |             | the text string. The underlined character is used for mnemonic |
   |             | activation if "Notebook.enable_traversal()" is called.         |
   +-------------+----------------------------------------------------------------+


Tab Identifiers
---------------

The tab_id present in several methods of "ttk.Notebook" may take any
of the following forms:

* An integer between zero and the number of tabs

* The name of a child window

* A positional specification of the form "@x,y", which identifies the
  tab

* The literal string "current", which identifies the currently-
  selected tab

* The literal string "end", which returns the number of tabs (only
  valid for "Notebook.index()")


Virtual Events
--------------

This widget generates a **<<NotebookTabChanged>>** virtual event after
a new tab is selected.


ttk.Notebook
------------

class tkinter.ttk.Notebook

   add(child, **kw)

      Adds a new tab to the notebook.

      If window is currently managed by the notebook but hidden, it is
      restored to its previous position.

      See Tab Options for the list of available options.

   forget(tab_id)

      Removes the tab specified by *tab_id*, unmaps and unmanages the
      associated window.

   hide(tab_id)

      Hides the tab specified by *tab_id*.

      The tab will not be displayed, but the associated window remains
      managed by the notebook and its configuration remembered. Hidden
      tabs may be restored with the "add()" command.

   identify(x, y)

      Returns the name of the tab element at position *x*, *y*, or the
      empty string if none.

   index(tab_id)

      Returns the numeric index of the tab specified by *tab_id*, or
      the total number of tabs if *tab_id* is the string "end".

   insert(pos, child, **kw)

      Inserts a pane at the specified position.

      *pos* is either the string "end", an integer index, or the name
      of a managed child. If *child* is already managed by the
      notebook, moves it to the specified position.

      See Tab Options for the list of available options.

   select(tab_id=None)

      Selects the specified *tab_id*.

      The associated child window will be displayed, and the
      previously-selected window (if different) is unmapped. If
      *tab_id* is omitted, returns the widget name of the currently
      selected pane.

   tab(tab_id, option=None, **kw)

      Query or modify the options of the specific *tab_id*.

      If *kw* is not given, returns a dictionary of the tab option
      values. If *option* is specified, returns the value of that
      *option*. Otherwise, sets the options to the corresponding
      values.

   tabs()

      Returns a list of windows managed by the notebook.

   enable_traversal()

      Enable keyboard traversal for a toplevel window containing this
      notebook.

      This will extend the bindings for the toplevel window containing
      the notebook as follows:

      * "Control-Tab": selects the tab following the currently
        selected one.

      * "Shift-Control-Tab": selects the tab preceding the currently
        selected one.

      * "Alt-K": where *K* is the mnemonic (underlined) character of
        any tab, will select that tab.

      Multiple notebooks in a single toplevel may be enabled for
      traversal, including nested notebooks. However, notebook
      traversal only works properly if all panes have the notebook
      they are in as master.


Progressbar
===========

The "ttk.Progressbar" widget shows the status of a long-running
operation. It can operate in two modes:  1) the determinate mode which
shows the amount completed relative to the total amount of work to be
done and 2) the indeterminate mode which provides an animated display
to let the user know that work is progressing.


选项
----

This widget accepts the following specific options:

   +------------+-----------------------------------------------------------------+
   | 选项       | 描述                                                            |
   |============|=================================================================|
   | orient     | One of "horizontal" or "vertical". Specifies the orientation of |
   |            | the progress bar.                                               |
   +------------+-----------------------------------------------------------------+
   | length     | Specifies the length of the long axis of the progress bar       |
   |            | (width if horizontal, height if vertical).                      |
   +------------+-----------------------------------------------------------------+
   | 模式       | One of "determinate" or "indeterminate".                        |
   +------------+-----------------------------------------------------------------+
   | maximum    | A number specifying the maximum value. Defaults to 100.         |
   +------------+-----------------------------------------------------------------+
   | 值         | The current value of the progress bar. In "determinate" mode,   |
   |            | this represents the amount of work completed. In                |
   |            | "indeterminate" mode, it is interpreted as modulo *maximum*;    |
   |            | that is, the progress bar completes one "cycle" when its value  |
   |            | increases by *maximum*.                                         |
   +------------+-----------------------------------------------------------------+
   | variable   | A name which is linked to the option value. If specified, the   |
   |            | value of the progress bar is automatically set to the value of  |
   |            | this name whenever the latter is modified.                      |
   +------------+-----------------------------------------------------------------+
   | phase      | Read-only option. The widget periodically increments the value  |
   |            | of this option whenever its value is greater than 0 and, in     |
   |            | determinate mode, less than maximum. This option may be used by |
   |            | the current theme to provide additional animation effects.      |
   +------------+-----------------------------------------------------------------+


ttk.Progressbar
---------------

class tkinter.ttk.Progressbar

   start(interval=None)

      Begin autoincrement mode: schedules a recurring timer event that
      calls "Progressbar.step()" every *interval* milliseconds. If
      omitted, *interval* defaults to 50 milliseconds.

   step(amount=None)

      Increments the progress bar's value by *amount*.

      *amount* defaults to 1.0 if omitted.

   stop()

      Stop autoincrement mode: cancels any recurring timer event
      initiated by "Progressbar.start()" for this progress bar.


Separator
=========

The "ttk.Separator" widget displays a horizontal or vertical separator
bar.

It has no other methods besides the ones inherited from "ttk.Widget".


选项
----

This widget accepts the following specific option:

   +----------+------------------------------------------------------------------+
   | 选项     | 描述                                                             |
   |==========|==================================================================|
   | orient   | One of "horizontal" or "vertical". Specifies the orientation of  |
   |          | the separator.                                                   |
   +----------+------------------------------------------------------------------+


Sizegrip
========

The "ttk.Sizegrip" widget (also known as a grow box) allows the user
to resize the containing toplevel window by pressing and dragging the
grip.

This widget has neither specific options nor specific methods, besides
the ones inherited from "ttk.Widget".


Platform-specific notes
-----------------------

* On MacOS X, toplevel windows automatically include a built-in size
  grip by default. Adding a "Sizegrip" is harmless, since the built-in
  grip will just mask the widget.


Bugs
----

* If the containing toplevel's position was specified relative to the
  right or bottom of the screen (e.g. ....), the "Sizegrip" widget
  will not resize the window.

* This widget supports only "southeast" resizing.


Treeview
========

The "ttk.Treeview" widget displays a hierarchical collection of items.
Each item has a textual label, an optional image, and an optional list
of data values. The data values are displayed in successive columns
after the tree label.

The order in which data values are displayed may be controlled by
setting the widget option "displaycolumns". The tree widget can also
display column headings. Columns may be accessed by number or symbolic
names listed in the widget option columns. See Column Identifiers.

Each item is identified by a unique name. The widget will generate
item IDs if they are not supplied by the caller. There is a
distinguished root item, named "{}". The root item itself is not
displayed; its children appear at the top level of the hierarchy.

Each item also has a list of tags, which can be used to associate
event bindings with individual items and control the appearance of the
item.

The Treeview widget supports horizontal and vertical scrolling,
according to the options described in Scrollable Widget Options and
the methods "Treeview.xview()" and "Treeview.yview()".


选项
----

This widget accepts the following specific options:

   +------------------+----------------------------------------------------------+
   | 选项             | 描述                                                     |
   |==================|==========================================================|
   | columns          | A list of column identifiers, specifying the number of   |
   |                  | columns and their names.                                 |
   +------------------+----------------------------------------------------------+
   | displaycolumns   | A list of column identifiers (either symbolic or integer |
   |                  | indices) specifying which data columns are displayed and |
   |                  | the order in which they appear, or the string "#all".    |
   +------------------+----------------------------------------------------------+
   | height           | Specifies the number of rows which should be visible.    |
   |                  | Note: the requested width is determined from the sum of  |
   |                  | the column widths.                                       |
   +------------------+----------------------------------------------------------+
   | padding          | Specifies the internal padding for the widget. The       |
   |                  | padding is a list of up to four length specifications.   |
   +------------------+----------------------------------------------------------+
   | selectmode       | Controls how the built-in class bindings manage the      |
   |                  | selection. One of "extended", "browse" or "none". If set |
   |                  | to "extended" (the default), multiple items may be       |
   |                  | selected. If "browse", only a single item will be        |
   |                  | selected at a time. If "none", the selection will not be |
   |                  | changed.  Note that the application code and tag         |
   |                  | bindings can set the selection however they wish,        |
   |                  | regardless of the value  of this option.                 |
   +------------------+----------------------------------------------------------+
   | show             | A list containing zero or more of the following values,  |
   |                  | specifying which elements of the tree to display.  *     |
   |                  | tree: display tree labels in column #0.  * headings:     |
   |                  | display the heading row.  The default is "tree           |
   |                  | headings", i.e., show all elements.  **Note**: Column #0 |
   |                  | always refers to the tree column, even if show="tree" is |
   |                  | not specified.                                           |
   +------------------+----------------------------------------------------------+


Item Options
------------

The following item options may be specified for items in the insert
and item widget commands.

   +----------+-----------------------------------------------------------------+
   | 选项     | 描述                                                            |
   |==========|=================================================================|
   | text     | The textual label to display for the item.                      |
   +----------+-----------------------------------------------------------------+
   | image    | A Tk Image, displayed to the left of the label.                 |
   +----------+-----------------------------------------------------------------+
   | values   | The list of values associated with the item.  Each item should  |
   |          | have the same number of values as the widget option columns. If |
   |          | there are fewer values than columns, the remaining values are   |
   |          | assumed empty. If there are more values than columns, the extra |
   |          | values are ignored.                                             |
   +----------+-----------------------------------------------------------------+
   | open     | "True"/"False" value indicating whether the item's children     |
   |          | should be displayed or hidden.                                  |
   +----------+-----------------------------------------------------------------+
   | tags     | A list of tags associated with this item.                       |
   +----------+-----------------------------------------------------------------+


Tag Options
-----------

The following options may be specified on tags:

   +--------------+-------------------------------------------------------------+
   | 选项         | 描述                                                        |
   |==============|=============================================================|
   | foreground   | Specifies the text foreground color.                        |
   +--------------+-------------------------------------------------------------+
   | background   | Specifies the cell or item background color.                |
   +--------------+-------------------------------------------------------------+
   | font         | Specifies the font to use when drawing text.                |
   +--------------+-------------------------------------------------------------+
   | image        | Specifies the item image, in case the item's image option   |
   |              | is empty.                                                   |
   +--------------+-------------------------------------------------------------+


Column Identifiers
------------------

Column identifiers take any of the following forms:

* A symbolic name from the list of columns option.

* An integer n, specifying the nth data column.

* A string of the form #n, where n is an integer, specifying the nth
  display column.

註解：

* Item's option values may be displayed in a different order than the
  order in which they are stored.

* Column #0 always refers to the tree column, even if show="tree" is
  not specified.

A data column number is an index into an item's option values list; a
display column number is the column number in the tree where the
values are displayed. Tree labels are displayed in column #0. If
option displaycolumns is not set, then data column n is displayed in
column #n+1. Again, **column #0 always refers to the tree column**.


Virtual Events
--------------

The Treeview widget generates the following virtual events.

   +----------------------+----------------------------------------------------+
   | Event                | 描述                                               |
   |======================|====================================================|
   | <<TreeviewSelect>>   | Generated whenever the selection changes.          |
   +----------------------+----------------------------------------------------+
   | <<TreeviewOpen>>     | Generated just before settings the focus item to   |
   |                      | open=True.                                         |
   +----------------------+----------------------------------------------------+
   | <<TreeviewClose>>    | Generated just after setting the focus item to     |
   |                      | open=False.                                        |
   +----------------------+----------------------------------------------------+

The "Treeview.focus()" and "Treeview.selection()" methods can be used
to determine the affected item or items.


ttk.Treeview
------------

class tkinter.ttk.Treeview

   bbox(item, column=None)

      Returns the bounding box (relative to the treeview widget's
      window) of the specified *item* in the form (x, y, width,
      height).

      If *column* is specified, returns the bounding box of that cell.
      If the *item* is not visible (i.e., if it is a descendant of a
      closed item or is scrolled offscreen), returns an empty string.

   get_children(item=None)

      Returns the list of children belonging to *item*.

      If *item* is not specified, returns root children.

   set_children(item, *newchildren)

      Replaces *item*'s child with *newchildren*.

      Children present in *item* that are not present in *newchildren*
      are detached from the tree. No items in *newchildren* may be an
      ancestor of *item*. Note that not specifying *newchildren*
      results in detaching *item*'s children.

   column(column, option=None, **kw)

      Query or modify the options for the specified *column*.

      If *kw* is not given, returns a dict of the column option
      values. If *option* is specified then the value for that
      *option* is returned. Otherwise, sets the options to the
      corresponding values.

      The valid options/values are:

      * id
           Returns the column name. This is a read-only option.

      * anchor: One of the standard Tk anchor values.
           Specifies how the text in this column should be aligned
           with respect to the cell.

      * minwidth: width
           The minimum width of the column in pixels. The treeview
           widget will not make the column any smaller than specified
           by this option when the widget is resized or the user drags
           a column.

      * stretch: "True"/"False"
           Specifies whether the column's width should be adjusted
           when the widget is resized.

      * width: width
           The width of the column in pixels.

      To configure the tree column, call this with column = "#0"

   delete(*items)

      Delete all specified *items* and all their descendants.

      The root item may not be deleted.

   detach(*items)

      Unlinks all of the specified *items* from the tree.

      The items and all of their descendants are still present, and
      may be reinserted at another point in the tree, but will not be
      displayed.

      The root item may not be detached.

   exists(item)

      Returns "True" if the specified *item* is present in the tree.

   focus(item=None)

      If *item* is specified, sets the focus item to *item*.
      Otherwise, returns the current focus item, or '' if there is
      none.

   heading(column, option=None, **kw)

      Query or modify the heading options for the specified *column*.

      If *kw* is not given, returns a dict of the heading option
      values. If *option* is specified then the value for that
      *option* is returned. Otherwise, sets the options to the
      corresponding values.

      The valid options/values are:

      * text: text
           The text to display in the column heading.

      * image: imageName
           Specifies an image to display to the right of the column
           heading.

      * anchor: anchor
           Specifies how the heading text should be aligned. One of
           the standard Tk anchor values.

      * command: callback
           A callback to be invoked when the heading label is pressed.

      To configure the tree column heading, call this with column =
      "#0".

   identify(component, x, y)

      Returns a description of the specified *component* under the
      point given by *x* and *y*, or the empty string if no such
      *component* is present at that position.

   identify_row(y)

      Returns the item ID of the item at position *y*.

   identify_column(x)

      Returns the data column identifier of the cell at position *x*.

      The tree column has ID #0.

   identify_region(x, y)

      Returns one of:

      +-------------+----------------------------------------+
      | region      | meaning                                |
      |=============|========================================|
      | heading     | Tree heading area.                     |
      +-------------+----------------------------------------+
      | separator   | Space between two columns headings.    |
      +-------------+----------------------------------------+
      | tree        | The tree area.                         |
      +-------------+----------------------------------------+
      | cell        | A data cell.                           |
      +-------------+----------------------------------------+

      Availability: Tk 8.6.

   identify_element(x, y)

      Returns the element at position *x*, *y*.

      Availability: Tk 8.6.

   index(item)

      Returns the integer index of *item* within its parent's list of
      children.

   insert(parent, index, iid=None, **kw)

      Creates a new item and returns the item identifier of the newly
      created item.

      *parent* is the item ID of the parent item, or the empty string
      to create a new top-level item. *index* is an integer, or the
      value "end", specifying where in the list of parent's children
      to insert the new item. If *index* is less than or equal to
      zero, the new node is inserted at the beginning; if *index* is
      greater than or equal to the current number of children, it is
      inserted at the end. If *iid* is specified, it is used as the
      item identifier; *iid* must not already exist in the tree.
      Otherwise, a new unique identifier is generated.

      See Item Options for the list of available points.

   item(item, option=None, **kw)

      Query or modify the options for the specified *item*.

      If no options are given, a dict with options/values for the item
      is returned. If *option* is specified then the value for that
      option is returned. Otherwise, sets the options to the
      corresponding values as given by *kw*.

   move(item, parent, index)

      Moves *item* to position *index* in *parent*'s list of children.

      It is illegal to move an item under one of its descendants. If
      *index* is less than or equal to zero, *item* is moved to the
      beginning; if greater than or equal to the number of children,
      it is moved to the end. If *item* was detached it is reattached.

   next(item)

      Returns the identifier of *item*'s next sibling, or '' if *item*
      is the last child of its parent.

   parent(item)

      Returns the ID of the parent of *item*, or '' if *item* is at
      the top level of the hierarchy.

   prev(item)

      Returns the identifier of *item*'s previous sibling, or '' if
      *item* is the first child of its parent.

   reattach(item, parent, index)

      An alias for "Treeview.move()".

   see(item)

      Ensure that *item* is visible.

      Sets all of *item*'s ancestors open option to "True", and
      scrolls the widget if necessary so that *item* is within the
      visible portion of the tree.

   selection()

      Returns a tuple of selected items.

      3.8 版更變: "selection()" no longer takes arguments.  For
      changing the selection state use the following selection
      methods.

   selection_set(*items)

      *items* becomes the new selection.

      3.6 版更變: *items* can be passed as separate arguments, not
      just as a single tuple.

   selection_add(*items)

      Add *items* to the selection.

      3.6 版更變: *items* can be passed as separate arguments, not
      just as a single tuple.

   selection_remove(*items)

      Remove *items* from the selection.

      3.6 版更變: *items* can be passed as separate arguments, not
      just as a single tuple.

   selection_toggle(*items)

      Toggle the selection state of each item in *items*.

      3.6 版更變: *items* can be passed as separate arguments, not
      just as a single tuple.

   set(item, column=None, value=None)

      With one argument, returns a dictionary of column/value pairs
      for the specified *item*. With two arguments, returns the
      current value of the specified *column*. With three arguments,
      sets the value of given *column* in given *item* to the
      specified *value*.

   tag_bind(tagname, sequence=None, callback=None)

      Bind a callback for the given event *sequence* to the tag
      *tagname*. When an event is delivered to an item, the callbacks
      for each of the item's tags option are called.

   tag_configure(tagname, option=None, **kw)

      Query or modify the options for the specified *tagname*.

      If *kw* is not given, returns a dict of the option settings for
      *tagname*. If *option* is specified, returns the value for that
      *option* for the specified *tagname*. Otherwise, sets the
      options to the corresponding values for the given *tagname*.

   tag_has(tagname, item=None)

      If *item* is specified, returns 1 or 0 depending on whether the
      specified *item* has the given *tagname*. Otherwise, returns a
      list of all items that have the specified tag.

      Availability: Tk 8.6

   xview(*args)

      Query or modify horizontal position of the treeview.

   yview(*args)

      Query or modify vertical position of the treeview.


Ttk Styling
===========

Each widget in "ttk" is assigned a style, which specifies the set of
elements making up the widget and how they are arranged, along with
dynamic and default settings for element options. By default the style
name is the same as the widget's class name, but it may be overridden
by the widget's style option. If you don't know the class name of a
widget, use the method "Misc.winfo_class()"
(somewidget.winfo_class()).

也參考:

  Tcl'2004 conference presentation
     This document explains how the theme engine works

class tkinter.ttk.Style

   This class is used to manipulate the style database.

   configure(style, query_opt=None, **kw)

      Query or set the default value of the specified option(s) in
      *style*.

      Each key in *kw* is an option and each value is a string
      identifying the value for that option.

      For example, to change every default button to be a flat button
      with some padding and a different background color:

         from tkinter import ttk
         import tkinter

         root = tkinter.Tk()

         ttk.Style().configure("TButton", padding=6, relief="flat",
            background="#ccc")

         btn = ttk.Button(text="Sample")
         btn.pack()

         root.mainloop()

   map(style, query_opt=None, **kw)

      Query or sets dynamic values of the specified option(s) in
      *style*.

      Each key in *kw* is an option and each value should be a list or
      a tuple (usually) containing statespecs grouped in tuples,
      lists, or some other preference. A statespec is a compound of
      one or more states and then a value.

      An example may make it more understandable:

         import tkinter
         from tkinter import ttk

         root = tkinter.Tk()

         style = ttk.Style()
         style.map("C.TButton",
             foreground=[('pressed', 'red'), ('active', 'blue')],
             background=[('pressed', '!disabled', 'black'), ('active', 'white')]
             )

         colored_btn = ttk.Button(text="Test", style="C.TButton").pack()

         root.mainloop()

      Note that the order of the (states, value) sequences for an
      option does matter, if the order is changed to "[('active',
      'blue'), ('pressed', 'red')]" in the foreground option, for
      example, the result would be a blue foreground when the widget
      were in active or pressed states.

   lookup(style, option, state=None, default=None)

      Returns the value specified for *option* in *style*.

      If *state* is specified, it is expected to be a sequence of one
      or more states. If the *default* argument is set, it is used as
      a fallback value in case no specification for option is found.

      To check what font a Button uses by default:

         from tkinter import ttk

         print(ttk.Style().lookup("TButton", "font"))

   layout(style, layoutspec=None)

      Define the widget layout for given *style*. If *layoutspec* is
      omitted, return the layout specification for given style.

      *layoutspec*, if specified, is expected to be a list or some
      other sequence type (excluding strings), where each item should
      be a tuple and the first item is the layout name and the second
      item should have the format described in Layouts.

      To understand the format, see the following example (it is not
      intended to do anything useful):

         from tkinter import ttk
         import tkinter

         root = tkinter.Tk()

         style = ttk.Style()
         style.layout("TMenubutton", [
            ("Menubutton.background", None),
            ("Menubutton.button", {"children":
                [("Menubutton.focus", {"children":
                    [("Menubutton.padding", {"children":
                        [("Menubutton.label", {"side": "left", "expand": 1})]
                    })]
                })]
            }),
         ])

         mbtn = ttk.Menubutton(text='Text')
         mbtn.pack()
         root.mainloop()

   element_create(elementname, etype, *args, **kw)

      Create a new element in the current theme, of the given *etype*
      which is expected to be either "image", "from" or "vsapi". The
      latter is only available in Tk 8.6a for Windows XP and Vista and
      is not described here.

      If "image" is used, *args* should contain the default image name
      followed by statespec/value pairs (this is the imagespec), and
      *kw* may have the following options:

         * border=padding
              padding is a list of up to four integers, specifying the
              left, top, right, and bottom borders, respectively.

         * height=height
              Specifies a minimum height for the element. If less than
              zero, the base image's height is used as a default.

         * padding=padding
              Specifies the element's interior padding. Defaults to
              border's value if not specified.

         * sticky=spec
              Specifies how the image is placed within the final
              parcel. spec contains zero or more characters "n", "s",
              "w", or "e".

         * width=width
              Specifies a minimum width for the element. If less than
              zero, the base image's width is used as a default.

      If "from" is used as the value of *etype*, "element_create()"
      will clone an existing element. *args* is expected to contain a
      themename, from which the element will be cloned, and optionally
      an element to clone from. If this element to clone from is not
      specified, an empty element will be used. *kw* is discarded.

   element_names()

      Returns the list of elements defined in the current theme.

   element_options(elementname)

      Returns the list of *elementname*'s options.

   theme_create(themename, parent=None, settings=None)

      Create a new theme.

      It is an error if *themename* already exists. If *parent* is
      specified, the new theme will inherit styles, elements and
      layouts from the parent theme. If *settings* are present they
      are expected to have the same syntax used for
      "theme_settings()".

   theme_settings(themename, settings)

      Temporarily sets the current theme to *themename*, apply
      specified *settings* and then restore the previous theme.

      Each key in *settings* is a style and each value may contain the
      keys 'configure', 'map', 'layout' and 'element create' and they
      are expected to have the same format as specified by the methods
      "Style.configure()", "Style.map()", "Style.layout()" and
      "Style.element_create()" respectively.

      As an example, let's change the Combobox for the default theme a
      bit:

         from tkinter import ttk
         import tkinter

         root = tkinter.Tk()

         style = ttk.Style()
         style.theme_settings("default", {
            "TCombobox": {
                "configure": {"padding": 5},
                "map": {
                    "background": [("active", "green2"),
                                   ("!disabled", "green4")],
                    "fieldbackground": [("!disabled", "green3")],
                    "foreground": [("focus", "OliveDrab1"),
                                   ("!disabled", "OliveDrab2")]
                }
            }
         })

         combo = ttk.Combobox().pack()

         root.mainloop()

   theme_names()

      Returns a list of all known themes.

   theme_use(themename=None)

      If *themename* is not given, returns the theme in use.
      Otherwise, sets the current theme to *themename*, refreshes all
      widgets and emits a <<ThemeChanged>> event.


Layouts
-------

A layout can be just "None", if it takes no options, or a dict of
options specifying how to arrange the element. The layout mechanism
uses a simplified version of the pack geometry manager: given an
initial cavity, each element is allocated a parcel. Valid
options/values are:

   * side: whichside
        Specifies which side of the cavity to place the element; one
        of top, right, bottom or left. If omitted, the element
        occupies the entire cavity.

   * sticky: nswe
        Specifies where the element is placed inside its allocated
        parcel.

   * unit: 0 or 1
        If set to 1, causes the element and all of its descendants to
        be treated as a single element for the purposes of
        "Widget.identify()" et al. It's used for things like scrollbar
        thumbs with grips.

   * children: [sublayout... ]
        Specifies a list of elements to place inside the element. Each
        element is a tuple (or other sequence type) where the first
        item is the layout name, and the other is a Layout.
