Flexbox

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import panel as pn
pn.extension()

The FlexBox is a list-like layout (unlike GridSpec) that wraps objects into a CSS flex container. It has a list-like API with methods to append, extend, clear, insert, pop, remove and __setitem__, which make it possible to interactively update and modify the layout and exposes all the CSS options for controlling the behavior and layout of the flex box.

For a detailed introduction to CSS flex boxes, see this guide.

Parameters:

For layout and styling related parameters see the customization user guide.

  • align_content (str): Defines how a flex container’s lines align when there is extra space in the cross-axis. One of ‘normal’, ‘flex-start’, ‘flex-end’, ‘center’, ‘space-between’, ‘space-around’, ‘space-evenly’, ‘stretch’, ‘start’, ‘end’, ‘baseline’, ‘first baseline’ and ‘last baseline’.

  • align_items (str): Defines the default behavior for how flex items are laid out along the cross axis on the current line. Same options as align_content.

  • flex_direction (str): This establishes the main-axis, thus defining the direction flex items are placed in the flex container. One of ‘row’, ‘row-reverse’, ‘column’, ‘column-reverse’.

  • flex_wrap (str): Whether and how to wrap items in the flex container. One of ‘nowrap’, ‘wrap’, ‘wrap-reverse’.

  • justify_content (str): Defines the alignment along the main axis. One of ‘flex-start’, ‘flex-end’, ‘center’, ‘space-between’, ‘space-around’, ‘space-evenly’, ‘start’, ‘end’, ‘left’, ‘right’.

  • objects (list): The list of objects to display in the WidgetBox. Should not generally be modified directly except when replaced in its entirety.


A FlexBox layout can either be instantiated as empty and populated after the fact or using a list of objects provided as positional arguments. If the objects are not already panel components they will each be converted to one using the pn.panel conversion method. By default the FlexBox has a flex_direction='row' and uses flex_wrap='wrap', which means items will flow in a row-wise manner

import random

rcolor = lambda: "#%06x" % random.randint(0, 0xFFFFFF)

box = pn.FlexBox(*[pn.pane.HTML(str(i), background=rcolor(), width=100, height=100) for i in range(24)])
box

We can flip the direction by setting the flex_direction parameter to 'column':

column_box = box.clone(flex_direction='column', height=450)
column_box

The other options including align_content, align_items, and justify_content control how items are spaced on the page, e.g. align_content declares how to distribute items along the cross-axis (i.e. along the row direction for a column based flexbox):

column_box.clone(align_content='space-evenly')

In general it is preferred to modify layouts only through the provided methods and avoid modifying the objects parameter directly. The one exception is when replacing the list of objects entirely, otherwise it is recommended to use the methods on the FlexBox itself to ensure that the rendered views of the FlexBox are rerendered in response to the change. As a simple example we might assign a new item to the box using a setitem operation:

color = pn.pane.HTML(str(5), background=rcolor(), width=100, height=100)
column_box[5] = color

To see the effect in a statically rendered page, we will display the box a second time:

column_box

In general a FlexBox does not have to be given a width, height or sizing_mode, allowing it to adapt to the size of its contents.

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Download this notebook from GitHub (right-click to download).