The DOM
The DOM (document object model) is a tree like data structure representing the web page displayed by the browser. PyScript interacts with the DOM to change the user interface and react to things happening in the browser.
There are currently two ways to interact with the DOM:
- Through the foreign function interface (FFI) to interact with objects found
in the browser's
globalThis
ordocument
objects. - Through the
pydom
module that acts as a Pythonic wrapper around the FFI and comes as standard with PyScript.
FFI
The foreign function interface (FFI) gives Python access to all the standard web capabilities and features, such as the browser's built-in web APIs.
This is available via the pyscript.window
module which is a proxy for
the main thread's globalThis
object, or pyscript.document
which is a proxy
for the website's document
object in JavaScript:
from pyscript import window, document
my_element = document.querySelector("#my-id")
my_element.innerText = window.location.hostname
The FFI creates proxy objects in Python linked to actual objects in JavaScript.
The proxy objects in your Python code look and behave like Python
objects but have related JavaScript objects associated with them. It means the
API defined in JavaScript remains the same in Python, so any
browser based JavaScript APIs
or third party JavaScript libraries that expose objects in the web page's
globalThis
, will have exactly the same API in Python as in JavaScript.
The FFI automatically transforms Python and JavaScript objects into the
equivalent in the other language. For example, Python's boolean True
and
False
will become JavaScript's true
and false
, while a JavaScript array
of strings and integers, ["hello", 1, 2, 3]
becomes a Python list of the
equivalent values: ["hello", 1, 2, 3]
.
Info
Instantiating classes into objects is an interesting special case that the FFI expects you to handle.
If you wish to instantiate a JavaScript class in your Python
code, you need to call the class's new
method:
The underlying reason for this is simply JavaScript and Python do
instantiation very differently. By explicitly calling the JavaScript
class's new
method PyScript both signals and honours this difference.
PyDom
The Standard Web APIs are massive and not always very user-friendly. PyDom
is a
Python modue that exposes the power of the web with an easy and idiomatic Pythonic
interface on top.
While the FFI interface described above focuses on giving full access to
the entire Standard Web APIs, pydom
focuses on providing a small, intuitive and yet
powerful API that priotirizes common use cases fist. For this reason, it's first
layer is simple and intuitive (but limited to the most common use cases), but pydom
also provides a secondary layer that can be used to directly use full FFI interface
of a specific element.
It does not aim to replace the regular Web [Javascript] API nor to be as wide and offer feature parity. On the contrary, it's intentionally small and focused on the most popular use cases while still providing [a backdoor] access to the full JS API.
Pydom
draws inspiration from popular Python APIs/Libraries known to be friendly and
easy to learn, and other successful projects related the web as well (for isntance,
JQuery
was a good source of inspiration).
Warning
PyDom is currently a work in progress.
We welcome feedback and suggestions.
Core Concepts
Pydom
builds on topic of very few and simple core concepts:
Element
: any component that is part of a web page. This is a rough abstraction of an HTMLElement. In general,pydom
elements always map to an underlyingHTML
Element
in a we pageElementCollection
: a collection of one or moreElements
. It is a rough abstraction of a HTMLCollection.- Querying: a method to query elements on a page based on a
selector. Pydom supports
standard HTML DOM query selectors to locate DOM elements as other native
JavaScript
methods likequerySelector
orquerySelectorAll
.
Following, we'll look into each one of these aspects a bit more in detail.
Element
pydom
Element
is simply just an abstraction of a tranditional Element
in a web page.
Every Element
always maps to an underlying JavaScript
Element
in a web page. These 2
elements are always in sync and any change of state in one is reflect into the other.
Creating a new element
New elements can be created by using the pydom.create
method and passing the type of element
being crated. Here's an example of what it looks like:
(To execute and explore the following code, click on the "load" button. The result will be conveniently displayed in the box on the below of the code example)
from pyweb import pydom
# Creating an element directly from pydom creates an unbounded element.
new_div = pydom.create("div")
# Creating an element from another element automatically creates that element
# as a child of the original element
new_p = new_div.create("p", classes=["code-description"], html="Ciao PyScripters!")
# elements can be appended to any other element on the page
pydom['#element-creation-example'][0].append(new_div)
Result will go here
For more details about pydom.create
please refer to its reference documentation.
Setting the content of an element
The Element interface offers 2 main ways to set an element content: the html
and the
content
attributes:
content
: sets theinnerHTML
field via the PyScriptdisplay
function. This takes care of properly rendering the object being passed based on the object mimetype. So, for instance, if the objects is an image, it'll be properly rendered on the elementhtml
: directly sets theinnerHTML
field of the underlying element without attemnpting any conversion.
In general, we suggest using content
directly as it'll take care of most use cases without
requiring any extra logic from the user.
Changing the element style
Elements have a style
attribute that can be used to change the element style rules.
The style attribyte can be used as a dictionary and, to set a style rule for the element,
simply set the correct key on the .style
attribute. For instance, the following
code changes the background color of the element just created in the example above:
to remove a specific style key, simply use the pop
method as you'd to to remove
a key from a dictionary:
In addition to the dictionary interface to explicitly set CSS rules, the style
attribute
also offers a convenient visible
property that can be use show/hide an element.
Other useful aspects of the Element API
append
: method to append a new child to the element.children
: list of the children of the element.value
: allows to set thevalue
attribute of an element.clone
: method that creates a clone of the element. NODE: The clone elements will not be attached to any element.show_me
: method to scroll the page to where the element is placed.
ElementCollection
Element Collections represent a collection of elements typically returned from a query. For instance:
In the example above, paragraphs
is an ElementCollection
that maps to all p
elements in the page.
As any collections, ElementCollection
can be used to iterate over a collection of elements or to pick
specific elements or slices of elements in the collection. For instance:
for element in paragraphs:
display(element.html)
# let's now display only the last 2 elements
for element in paragraphs[-2:]:
display(element.html)
Interacting with an ElementCollection
Besides from allowing operations as an iterable object, ElementCollection
objects also offer a few
convenient methods to directly interact with th elements in the collection. For instance, it's possible
to ask for specific attributes of the elements in the collection directly:
The example above displays a list with the value of the html
attribute for all the elements in the
paragraphs
collection.
The same way we can read attributes, we can also set an attribute directly in the collection. For instance, you can directly set the html content of all the elements in the collection
or perhaps change their style
ElementCollection
currently support the following attributes:
style
: just like inElement
, this proxy attribute can be used to change the style of the elements in a collection by setting the proper CSS rules, usingstyle
with the same API as a dictionary.html
: allows to change thehtml
attribute on all the elements of a collection.value
: allows to change thevalue
attribute on all the elements of a collection.