.. include:: headings.inc


.. _sizers overview:

=============================================
|phoenix_title|  **Sizers Overview**
=============================================


Sizers, as represented by the :ref:`wx.Sizer` class and its
descendants in the wxPython class hierarchy, have become the method of
choice to define the layout of controls in dialogs in wxPython because
of their ability to create visually appealing dialogs independent of
the platform, taking into account the differences in size and style of
the individual controls.  Editors such as wxDesigner, DialogBlocks,
XRCed and wxWorkshop create dialogs based exclusively on sizers,
practically forcing the user to create platform independent layouts
without compromises.

The next section describes and shows what can be done with sizers. The
following sections briefly describe how to program with individual
sizer classes.


The Idea Behind Sizers
----------------------

The layout algorithm used by sizers in wxPython is closely related to
layout systems in other GUI toolkits, such as Java's AWT, the GTK
toolkit or the Qt toolkit. It is based upon the idea of individual
subwindows reporting their minimal required size and their ability to
get stretched if the size of the parent window has changed. This will
most often mean that the programmer does not set the start-up size of
a dialog, the dialog will rather be assigned a sizer and this sizer
will be queried about the recommended size. This sizer in turn will
query its children (which can be normal windows, empty space or other
sizers) so that a hierarchy of sizers can be constructed. Note that
:ref:`wx.Sizer` does not derive from :ref:`wx.Window` and thus does
not interfere with tab ordering and requires very few resources
compared to a real window on screen.

What makes sizers so well fitted for use in wxPython is the fact that
every control reports its own minimal size and the algorithm can
handle differences in font sizes or different window (dialog item)
sizes on different platforms without problems. For example, if the
standard font as well as the overall design of Linux/GTK widgets
requires more space than on Windows, the initial dialog size will
automatically be bigger on Linux/GTK than on Windows.

There are currently five different kinds of sizers available in
wxPython. Each represents either a certain way to lay out dialog items
in a dialog or it fulfills a special task such as wrapping a static
box around a dialog item (or another sizer). These sizers will be
discussed one by one in the text below. For more detailed information
on how to use sizers programmatically, please refer to the section
:ref:`Programming with BoxSizer <programming with boxsizer>`.


Common Features
---------------

All sizers are containers, that is, they are used to lay out one
dialog item (or several dialog items), which they contain. Such items
are sometimes referred to as the children of the sizer. Independent of
how the individual sizers lay out their children, all children have
certain features in common:

**A minimal size**: This minimal size is usually identical to the
initial size of the controls and may either be set explicitly in the
:ref:`wx.Size` field of the control constructor or may be calculated
by wxPython, typically by setting the height and/or the width of the
item to -1. Note that only some controls can calculate their size
(such as a checkbox) whereas others (such as a listbox) don't have any
natural width or height and thus require an explicit size. Some
controls can calculate their height, but not their width (e.g. a
single line text control):


.. figure:: _static/images/overviews/overview_sizer_04.png
   :align: center


|


**A border**: The border is just empty space and is used to separate
dialog items in a dialog. This border can either be all around, or at
any combination of sides such as only above and below the control. The
thickness of this border must be set explicitly, typically 5
points. The following samples show dialogs with only one dialog item
(a button) and a border of 0, 5, and 10 pixels around the button:


.. figure:: _static/images/overviews/overview_sizer_02.png
   :align: center


|


**An alignment**: Often, a dialog item is given more space than its
minimal size plus its border. Depending on what flags are used for the
respective dialog item, the dialog item can be made to fill out the
available space entirely, i.e. it will grow to a size larger than the
minimal size, or it will be moved to either the centre of the
available space or to either side of the space. The following sample
shows a listbox and three buttons in a horizontal box sizer; one
button is centred, one is aligned at the top, one is aligned at the
bottom:


.. figure:: _static/images/overviews/overview_sizer_06.png
   :align: center


|


**A stretch factor**: If a sizer contains more than one child and it
is offered more space than its children and their borders need, the
question arises how to distribute the surplus space among the
children. For this purpose, a stretch factor may be assigned to each
child, where the default value of 0 indicates that the child will not
get more space than its requested minimum size. A value of more than
zero is interpreted in relation to the sum of all stretch factors in
the children of the respective sizer, i.e. if two children get a
stretch factor of 1, they will get half the extra space each
independent of whether one control has a minimal sizer inferior to the
other or not.  The following sample shows a dialog with three buttons,
the first one has a stretch factor of 1 and thus gets stretched,
whereas the other two buttons have a stretch factor of zero and keep
their initial width:


.. figure:: _static/images/overviews/overview_sizer_07.png
   :align: center


|


Within wxDesigner, this stretch factor gets set from the `Option`
menu.


`wx.Sizers` - the visual approach
---------------------------------


----------------------------
Basic way of adding a window
----------------------------

Let's take a look at :class:`wx.BoxSizer`.  This is the most simple
type of box sizer, and the way we add widgets to it is explained by
looking at the :meth:`wx.BoxSizer.Add` signature:

.. function:: Add(window, proportion=0, flag=0, border=0, userData=None)

   Appends a child to the sizer.

   :param `window`: a window, a spacer or another sizer to be added to the sizer. Its initial size
    (either set explicitly by the user or calculated internally) is interpreted as the minimal and
    in many cases also the initial size.
   :param int proportion: this parameter is used in :class:`wx.BoxSizer` to indicate if a child of a sizer
    can change its size in the main orientation of the :class:`wx.BoxSizer` - where 0 stands for not changeable
    and a value of more than zero is interpreted relative to the value of other children of the same
    :class:`wx.BoxSizer`. For example, you might have a horizontal :class:`wx.BoxSizer` with three children, two
    of which are supposed to change their size with the sizer. Then the two stretchable windows would
    get a value of 1 each to make them grow and shrink equally with the sizer's horizontal dimension.
   :param int flag: OR-combination of flags affecting sizer's behaviour.
   :param int border: determines the border width, if the flag parameter is set to include any border flag.
   :param object userData: allows an extra object to be attached to the sizer item, for use in derived
    classes when sizing information is more complex than the proportion and flag will allow for.

   :rtype: :class:`wx.SizerItem`



Let's create a vertical sizer (children will be placed on top of each
other) and place two buttons in it.  All the "extra" parameters are
set to 0; we'll worry about them later.

.. figure:: _static/images/overviews/boxsizer1.png
   :class: floatright

::

    sizer = wx.BoxSizer(wx.VERTICAL)
    sizer.Add(wx.Button(self, -1, 'An extremely long button text'), 0, 0, 0)
    sizer.Add(wx.Button(self, -1, 'Small button'), 0, 0, 0)
    self.SetSizer(sizer)


You'll notice a couple of things about this:

* The buttons are just big enough to accommodate the text in them. In
  fact, any control placed into a sizer this way will appear at its
  minimum size unless we change the parameters.

* The window size is not changed to fit the sizer. This results in a
  lot of ugly empty space.


Let's worry about the second issue first. To make the window size more appropriate, we can set
the size hints to tell the enclosing window to adjust to the size of the sizer:

.. figure:: _static/images/overviews/boxsizer2.png
   :class: floatright

.. code-block:: python
   :emphasize-lines: 4

    sizer = wx.BoxSizer(wx.VERTICAL)
    sizer.Add(wx.Button(self, -1, 'An extremely long button text'), 0, 0, 0)
    sizer.Add(wx.Button(self, -1, 'Small button'), 0, 0, 0)
    sizer.SetSizeHints(self)
    self.SetSizer(sizer)

This is particularly useful in circumstances like this one, in which
the :class:`wx.Frame`\ 's default size would otherwise be much too big
or small to show most layouts in an aesthetically pleasing manner.

--------------------------
The `proportion` parameter
--------------------------

The first parameter to :meth:`wx.BoxSizer.Add` is obviously the
:class:`wx.Window` or :class:`wx.Sizer` that you are adding. The
second one (the `proportion`) defines how large the sizer's children
are in relation to each other. In a vertical sizer, this changes the
height; in a horizontal sizer, this changes the width. Here are some
examples:

.. list-table::
   :header-rows: 1
   :widths: 40 10
   :class: centertable

   * - Code

     - Resulting Image

   * - .. code-block:: python
          :emphasize-lines: 3,4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Second button is three times as tall as first button
          sizer.Add(wx.Button(self, -1, 'An extremely long button text'), 1, 0, 0)
          sizer.Add(wx.Button(self, -1, 'Small button'), 3, 0, 0)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)

     - .. figure:: _static/images/overviews/boxsizer3.png
          :align: left

   * - Same code as above, with window resized. Notice that the bottom
       button is still three times as tall as the top button.

     - .. figure:: _static/images/overviews/boxsizer31.png
          :align: left

   * - .. code-block:: python
          :emphasize-lines: 3,4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # First button is 3/2 the height of the second button
          sizer.Add(wx.Button(self, -1, 'An extremely long button text'), 3, 0, 0)
          sizer.Add(wx.Button(self, -1, 'Small button'), 2, 0, 0)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)

     - .. figure:: _static/images/overviews/boxsizer32.png
          :align: left


|

If one of the `proportion` parameters is 0, that :class:`wx.Window`
will be the minimum size, and the others will resize proportionally:

.. list-table::
   :header-rows: 1
   :widths: 40 10
   :class: centertable

   * - Code

     - Resulting Image

   * - .. code-block:: python
          :emphasize-lines: 4,5

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Third button is twice the size of the second button
          sizer.Add(wx.Button(self, -1, 'An extremely long button text'), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, 'Small button'), 1, 0, 0)
          sizer.Add(wx.Button(self, -1, 'Another button'), 2, 0, 0)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)

     - .. figure:: _static/images/overviews/boxsizer33.png
          :align: left

   * - Same code as above, with window resized. The top button (proportion 0) is still the minimum height,
       and the third button is still twice the height of the second.

     - .. figure:: _static/images/overviews/boxsizer34.png
          :align: left


This is especially useful when you want, for example, a button at the
bottom which is only as big as necessary, and some other control that
occupies the rest of the frame. To do so, give the button proportion 0
and the other control a number greater than 0. Mac users in particular
will appreciate you for not creating huge aqua-styled buttons.


-----------------------------------
The `flags` and `border` parameters
-----------------------------------

The `flag` argument accepted by :meth:`wx.Sizer.Add` is a
``OR``-combination of the following flags. Two main behaviours are
defined using these flags. One is the border around a window: the
`border` parameter determines the border width whereas the flags given
here determine which side(s) of the item that the border will be
added. The other flags determine how the sizer item behaves when the
space allotted to the sizer changes, and is somewhat dependent on the
specific kind of sizer used.

.. include:: rest_substitutions/tables/wx.Sizer.1.rst

|


Let's start with the simplest case: the alignment flags. These are
pretty self-explanatory.

.. list-table::
   :header-rows: 1
   :widths: 40 10
   :class: centertable

   * - Code

     - Resulting Image

   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Second button is right aligned
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 0, wx.ALIGN_RIGHT, 0)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer4.png
          :align: left


   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Second button is center-aligned
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 0, wx.ALIGN_CENTER, 0)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer41.png
          :align: left



Next is the ``wx.EXPAND`` flag. This is synonymous with ``wx.GROW``.

.. list-table::
   :header-rows: 1
   :widths: 40 10
   :class: centertable

   * - Code

     - Resulting Image

   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Second button expands to the whole parent's width
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 0, wx.EXPAND, 0)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer5.png
          :align: left



You can see that the first button takes its minimum size, and the second one grows to match it. This affects
controls in the opposite manner of the second parameter; ``wx.EXPAND`` in a vertical sizer causes horizontal
expansion, and in a horizontal sizer it causes vertical expansion.

Next is ``wx.SHAPED``. This flag ensures that the width and height of the object stay proportional to each other.
It doesn't make much sense for buttons, but can be excellent for bitmaps, which would be contorted or clipped
if not scaled proportionally.


.. list-table::
   :header-rows: 1
   :widths: 30 10
   :class: centertable

   * - Code

     - Resulting Image

   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Second button will scale proportionally
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 1, wx.SHAPED, 0)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer51.png
          :align: left

   * - Same code as above, with window resized. The width grew
       dramatically with the height. In fact, it didn't quite grow
       vertically the whole way because it couldn't maintain the
       correct ratio while doing so.

     - .. figure:: _static/images/overviews/boxsizer52.png
          :align: left


Finally, we have the border flags. These only make sense when the
`border` parameter is greater than 0, and describe the sides of the
control on which the border should appear. In order to demonstrate
this most clearly, we'll keep the ``wx.EXPAND`` flag.


.. list-table::
   :header-rows: 1
   :widths: 40 10
   :class: centertable

   * - Code

     - Resulting Image

   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Border size effects
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 0, wx.EXPAND | wx.LEFT, 20)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer53.png
          :align: left


   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Border size effects
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 0, wx.EXPAND | wx.LEFT | wx.RIGHT, 20)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer54.png
          :align: left


   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Border size effects
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 0, wx.EXPAND | wx.LEFT | wx.RIGHT | wx.TOP, 20)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer55.png
          :align: left

   * - .. code-block:: python
          :emphasize-lines: 4

          sizer = wx.BoxSizer(wx.VERTICAL)
          # Border size effects
          sizer.Add(wx.Button(self, -1, "An extremely long button text"), 0, 0, 0)
          sizer.Add(wx.Button(self, -1, "Small Button"), 0, wx.EXPAND | wx.ALL, 20)
          sizer.SetSizeHints(self)
          self.SetSizer(sizer)


     - .. figure:: _static/images/overviews/boxsizer56.png
          :align: left


You can see that the button is offset from the specified edges of the
sizer by the number of pixels that we specified in the `border`
parameter.


Hiding Controls Using Sizers
----------------------------

You can hide controls contained in sizers the same way you would hide
any control, using the :meth:`wx.Window.Show` method. However,
:ref:`wx.Sizer` also offers a separate method which can tell the sizer
not to consider that control in its size calculations. To hide a
window using the sizer, call :meth:`wx.Sizer.Show`. You must then call
`Layout` on the sizer to force an update.

This is useful when hiding parts of the interface, since you can avoid
removing the controls from the sizer and having to add them back
later.

.. note:: This is supported only by :ref:`wx.BoxSizer` and :ref:`wx.FlexGridSizer`.


--------
BoxSizer
--------

:ref:`wx.BoxSizer` can lay out its children either vertically or
horizontally, depending on what flag is being used in its constructor.
When using a vertical sizer, each child can be centered, aligned to
the right or aligned to the left. Correspondingly, when using a
horizontal sizer, each child can be centered, aligned at the bottom or
aligned at the top. The stretch factor described in the last paragraph
is used for the main orientation, i.e. when using a horizontal box
sizer, the stretch factor determines how much the child can be
stretched horizontally. The following sample shows the same dialog as
in the last sample, only the box sizer is a vertical box sizer now:

.. figure:: _static/images/overviews/overview_sizer_08.png
   :align: center


--------------
StaticBoxSizer
--------------

:class:`wx.StaticBoxSizer` is the same as a :class:`wx.BoxSizer`, but
surrounded by a static box. Here is a sample:


.. figure:: _static/images/overviews/overview_sizer_09.png
   :align: center


---------
GridSizer
---------

:ref:`wx.GridSizer` is a two-dimensional sizer. All children are given
the same size, which is the minimal size required by the biggest
child, in this case the text control in the left bottom border. Either
the number of columns or the number or rows is fixed and the grid
sizer will grow in the respectively other orientation if new children
are added:


.. figure:: _static/images/overviews/overview_sizer_10.png
   :align: center


For programming information, see :ref:`wx.GridSizer`.

-------------
FlexGridSizer
-------------

Another two-dimensional sizer derived from :ref:`wx.GridSizer`. The
width of each column and the height of each row are calculated
individually according to the minimal requirements from the
respectively biggest child. Additionally, columns and rows can be
declared to be stretchable if the sizer is assigned a size different
from the one it requested. The following sample shows the same dialog
as the one above, but using a flex grid sizer:


.. figure:: _static/images/overviews/overview_sizer_11.png
   :align: center



.. _programming with boxsizer:

Programming with BoxSizer
---------------------------

The basic idea behind a :ref:`wx.BoxSizer` is that windows will most
often be laid out in rather simple basic geometry, typically in a row
or a column or several hierarchies of either.

As an example, we will construct a dialog that will contain a text
field at the top and two buttons at the bottom. This can be seen as a
top-hierarchy column with the text at the top and buttons at the
bottom and a low-hierarchy row with an ``OK`` button to the left and a
``Cancel`` button to the right. In many cases (particularly dialogs
under Unix and normal frames) the main window will be resizable by the
user and this change of size will have to get propagated to its
children. In our case, we want the text area to grow with the dialog,
whereas the button shall have a fixed size. In addition, there will be
a thin border around all controls to make the dialog look nice and -
to make matter worse - the buttons shall be centred as the width of
the dialog changes.

It is the unique feature of a box sizer, that it can grow in both
directions (height and width) but can distribute its growth in the
main direction (horizontal for a row) `unevenly` among its
children. In our example case, the vertical sizer is supposed to
propagate all its height changes to only the text area, not to the
button area. This is determined by the `proportion` parameter when
adding a window (or another sizer) to a sizer. It is interpreted as a
weight factor, i.e. it can be zero, indicating that the window may not
be resized at all, or above zero. If several windows have a value
above zero, the value is interpreted relative to the sum of all weight
factors of the sizer, so when adding two windows with a value of 1,
they will both get resized equally much and each half as much as the
sizer owning them.  Then what do we do when a column sizer changes its
width? This behaviour is controlled by `flags` (the second parameter
of the `Add()` function): Zero or no flag indicates that the window
will preserve it is original size, ``wx.GROW`` flag (same as ``wx.EXPAND``)
forces the window to grow with the sizer, and ``wx.SHAPED`` flag tells
the window to change it is size proportionally, preserving original
aspect ratio. When ``wx.GROW`` flag is not used, the item can be aligned
within available space. ``wx.ALIGN_LEFT``, ``wx.ALIGN_TOP``,
``wx.ALIGN_RIGHT``, ``wx.ALIGN_BOTTOM``, ``wx.ALIGN_CENTER_HORIZONTAL`` and
``wx.ALIGN_CENTER_VERTICAL`` do what they say. ``wx.ALIGN_CENTRE`` (same as
``wx.ALIGN_CENTER``) is defined as (``wx.ALIGN_CENTER_HORIZONTAL`` |
``wx.ALIGN_CENTER_VERTICAL``). Default alignment is ``wx.ALIGN_LEFT`` |
``wx.ALIGN_TOP``.

As mentioned above, any window belonging to a sizer may have a border,
and it can be specified which of the four sides may have this border,
using the ``wx.TOP``, ``wx.LEFT``, ``wx.RIGHT`` and ``wx.BOTTOM``
constants or ``wx.ALL`` for all directions (and you may also use
``wx.NORTH``, ``wx.WEST`` etc. instead).  These flags can be used in
combination with the alignment flags above as the second parameter of
the `Add()` method using the binary or operator ``|``.  The sizer of
the border also must be made known, and it is the third parameter in
the `Add()` method. This means, that the entire behaviour of a sizer
and its children can be controlled by the three parameters of the
`Add()` method.

Example::

        # We want to get a dialog that is stretchable because it
        # has a text ctrl at the top and two buttons at the bottom.

        class MyDialog(wx.Dialog):

            def __init__(self, parent, id, title):

                wx.Dialog(parent, id, title, wx.DefaultPosition, wx.DefaultSize,
                          wx.DEFAULT_DIALOG_STYLE | wx.RESIZE_BORDER)

                topsizer = wx.BoxSizer(wx.VERTICAL)

                # create text ctrl with minimal size 100x60
                topsizer.Add(
                        wx.TextCtrl(self, -1, "My text.", wx.DefaultPosition, wx.Size(100,60), wx.TE_MULTILINE),
                        1,           # make vertically stretchable
                        wx.EXPAND |  # make horizontally stretchable
                        wx.ALL,      # and make border all around
                        10)          # set border width to 10

                button_sizer = wx.BoxSizer(wx.HORIZONTAL)
                button_sizer.Add(
                        wx.Button(self, wx.ID_OK, "OK"),
                        0,           # make horizontally unstretchable
                        wx.ALL,      # make border all around (implicit top alignment)
                        10)          # set border width to 10
                button_sizer.Add(
                        wx.Button(self, wx.ID_CANCEL, "Cancel"),
                        0,           # make horizontally unstretchable
                        wx.ALL,      # make border all around (implicit top alignment)
                        10)          # set border width to 10

                topsizer.Add(
                        button_sizer,
                        0,                # make vertically unstretchable
                        wx.ALIGN_CENTER)  # no border and centre horizontally

                self.SetSizerAndFit(topsizer) # use the sizer for layout and size window
                                              # accordingly and prevent it from being resized
                                              # to smaller size



Note that the new way of specifying flags to :ref:`wx.Sizer` is via
:ref:`wx.SizerFlags`. This class greatly eases the burden of passing
flags to a :ref:`wx.Sizer`.

Here's how you'd do the previous example with :ref:`wx.SizerFlags`::


        # We want to get a dialog that is stretchable because it
        # has a text ctrl at the top and two buttons at the bottom.

        class MyDialog(wx.Dialog):

            def __init__(self, parent, id, title):

                wx.Dialog(parent, id, title, wx.DefaultPosition, wx.DefaultSize,
                          wx.DEFAULT_DIALOG_STYLE | wx.RESIZE_BORDER)

                topsizer = wx.BoxSizer(wx.VERTICAL)

                # create text ctrl with minimal size 100x60
                topsizer.Add(
                        wx.TextCtrl(self, -1, "My text.", wx.DefaultPosition, wx.Size(100,60), wx.TE_MULTILINE),
                        wx.SizerFlags(1).Align().Expand().Border(wx.ALL, 10))

                button_sizer = wx.BoxSizer(wx.HORIZONTAL)
                button_sizer.Add(
                        wx.Button(self, wx.ID_OK, "OK"),
                        wx.SizerFlags(0).Align().Border(wx.ALL, 10))

                button_sizer.Add(
                        wx.Button(self, wx.ID_CANCEL, "Cancel"),
                        wx.SizerFlags(0).Align().Border(wx.ALL, 10))

                topsizer.Add(
                        button_sizer,
                        wx.SizerFlags(0).Center())

                self.SetSizerAndFit(topsizer) # use the sizer for layout and set size and hints



Other Types of Sizers
---------------------

:ref:`wx.GridSizer` is a sizer which lays out its children in a
two-dimensional table with all table fields having the same size, i.e.
the width of each field is the width of the widest child, the height
of each field is the height of the tallest child.

:ref:`wx.FlexGridSizer` is a sizer which lays out its children in a
two-dimensional table with all table fields in one row having the same
height and all fields in one column having the same width, but all
rows or all columns are not necessarily the same height or width as in
the :ref:`wx.GridSizer`.

:class:`wx.StaticBoxSizer` is a sizer derived from :ref:`wx.BoxSizer`
but adds a static box around the sizer. Note that this static box has
to be created separately.

:ref:`wx.GridBagSizer` is a rather special kind of sizer which, unlike
the other classes, allows to directly put the elements at the given
position in the sizer. Please see its documentation for more details.


CreateButtonSizer
-----------------

As a convenience, :meth:`wx.Dialog.CreateButtonSizer`\ (flags) can be
used to create a standard button sizer in which standard buttons are
displayed. The following flags can be passed to this method::

        wx.YES_NO     # Add Yes/No subpanel
        wx.YES        # return wx.ID_YES
        wx.NO         # return wx.ID_NO
        wx.NO_DEFAULT # make the wx.NO button the default,
                      # otherwise wx.YES or wx.OK button will be default

        wx.OK         # return wx.ID_OK
        wx.CANCEL     # return wx.ID_CANCEL
        wx.HELP       # return wx.ID_HELP

        wx.FORWARD    # return wx.ID_FORWARD
        wx.BACKWARD   # return wx.ID_BACKWARD
        wx.SETUP      # return wx.ID_SETUP
        wx.MORE       # return wx.ID_MORE