nativelayout (Python)

Python port of the nativelayout core. It follows the Kotlin core feature for feature (currently v1.2.0: <include>, identity inside for, <footer> and dock, position: absolute, background-image, object-fit).

• core/ pure Python, no Kivy: parser, expander, layout engine, differ, program side
• android/ Kivy host for Android (nativelayout/host)
• desktop/ Kivy host for the desktop (nativelayout/host)
• examples/ examples (contador/)

The Kivy hosts draw on a canvas; they do not build platform-native views.

Install

pip install nativelayout            # core only (pure Python, no dependencies)
pip install "nativelayout[kivy]"    # core + Kivy host

Requires Python 3.10 or newer. On Android, package with buildozer (requirements = python3,kivy,nativelayout).

nativelayout is a namespace package (no __init__.py at its root): the core is nativelayout.core and the Kivy host is nativelayout.host. The package published on PyPI carries the Android host (android/), which includes the stencil mask that rounds background-image corners. To work from the repository instead, put core and the folder of the host on sys.path.

Usage

import kivy  # noqa: F401  (Pydroid starts the Kivy window only if the opened file imports kivy)
from nativelayout.core.program import state, view, click
from nativelayout.host import run_app, file_loader

def screen():
    s = state({"n": 0})
    if click(".more"):
        s["n"] += 1
    return view("screen.nl", s)

run_app(file_loader("."), app=screen)

The host needs Kivy 2.x.

Tests

cd python/core
python -m unittest discover -s tests -t .

cd python/android
python -m unittest discover -s tests -t .

The core tests mirror the Kotlin ones (IncludeTest, FooterTest, AbsoluteTest). The host tests cover flex.py, which does not need Kivy.

Status of the host (v1.2.0)

Done: columns and rows, flex, gap, justify, align, wrap, header, footer and dock, dialogs, position: absolute (with z-index), background-image (background-size, background-position), object-fit, icons, gradients, shadows, rounded corners.

Not done yet:

• virtual lists draw all items (no recycling)
• animations: only the fade-in of the screen (slide-up and slide-left are missing)
• letter-spacing and overflow: hidden (clipping) are not applied
• the Android keyboard can cover fields (adjust softinput_mode)
• the Kivy drawing of background-image and object-fit has not been tried on a device yet