pymobile-framework 0.3.0

A small, fast and extensible Python framework for building Android applications.

PyMobile

Build real Android apps in pure Python.

Write a declarative UI, run one command, install the APK on your phone.

---

from pymobile import App, Button, Column, Label, Screen, Widget


class Home(Screen):
    title = "Hello"

    def __init__(self) -> None:
        super().__init__()
        self.taps = 0

    def build(self) -> Widget:
        self.counter = Label("Taps: 0")
        return Column(
            Label("Hello, Android!"),
            self.counter,
            Button("Tap me", on_press=self.on_tap),
            spacing=12,
        )

    def on_tap(self) -> None:
        self.taps += 1
        self.counter.text = f"Taps: {self.taps}"      # the screen redraws itself


App("Demo").run(Home())

pip install pymobile-framework
pymobile setup-sdk           # once per machine
pymobile build --native      # → build/demo-0.1.0.apk

That APK is signed, installable and runs a real CPython interpreter on the device. No Java, no Gradle, no Android Studio.

---

Table of contents

• Why PyMobile
• Installation
• Your first app
• How it works
• UI components
• Layout
• Styling
• Screens and navigation
• Updating the screen
• Notifications
• Vibration
• Permissions
• HTTP requests
• Events
• Timers
• Configuration reference
• Building an APK
• Application icon
• Installing on a phone
• Debugging
• Testing your app
• Error handling
• Desktop preview
• CLI reference
• Extending the framework
• Limitations
• FAQ
• Contributing

---

Why PyMobile

Real APKs	Signed with v1+v2+v3 schemes, containing classes.dex, resources.arsc and an embedded CPython 3.14 for ARM64.
Native views	Widgets become genuine TextView, Button, EditText, Switch, ProgressBar and LinearLayout instances — not a web view or a custom canvas.
Fast	About five seconds per build. An unchanged rebuild is instant.
Small setup	~800 MB of tooling, downloaded automatically. The NDK is not required.
Testable	Your whole app runs and is unit-testable on a desktop, with no emulator.
No dependencies	The runtime uses only the standard library, which keeps APKs small.

Verified on a physical device running Android 14.

---

Installation

Requirements: Python 3.10+, about 1 GB of free disk space, an Android 5.0+ device.

pip install pymobile-framework

The distribution is named py-mobile because pymobile on PyPI belongs to an unrelated project. The import name and the CLI command are still pymobile.

Then install the Android toolchain, once per machine:

pymobile setup-sdk

This downloads JDK 17 and the Android SDK (~800 MB) into ~/.andro. The NDK is not downloaded: a prebuilt native bridge (22 KB) ships inside the package. It is byte-identical for every application, so there is nothing to compile. If you want to rebuild it from C source anyway:

pymobile setup-sdk --with-ndk    # adds ~2 GB

Already have Android Studio? Point PyMobile at your existing SDK instead:

export ANDROID_HOME=~/Android/Sdk          # macOS/Linux
$env:ANDROID_HOME = "C:\...\Android\Sdk"   # Windows PowerShell

You need build-tools;34.0.0 and platforms;android-34.

If the pymobile command is not found

Common on Windows when pip's scripts directory is not on PATH. This form always works:

python -m pymobile build --native

Verify everything with:

pymobile doctor

---

Your first app

pymobile init myapp --name "My App" -p com.example.myapp
cd myapp
pymobile run                # preview on your machine
pymobile build --native     # produce the APK

init generates:

myapp/
├── main.py           # your application
├── pymobile.toml     # configuration
├── README.md
├── .gitignore
└── assets/           # images, fonts, data files

The smallest possible app:

from pymobile import App, Column, Label, Screen, Widget


class Home(Screen):
    def build(self) -> Widget:
        return Column(Label("Hello, Android!"))


App("My App").run(Home())

---

How it works

Three ideas explain everything else.

1. Widgets are descriptions, not views. Label("Hello") draws nothing. It is a node in a tree that serialises to JSON. A Java renderer converts that tree into real Android views and patches them in place on every update.

2. Everything platform-specific goes through a bridge.

Your Python code
       ↓
    Bridge ──┬── AndroidBridge   on device, through JNI
             └── StubBridge      on desktop, records every call

3. Therefore your app runs anywhere. On a laptop the stub bridge logs what would have happened; on a phone the same code vibrates and posts notifications. You never write if android: — the framework picks the implementation.

app = App("Demo")
print(app.platform)      # 'desktop' or 'android'
print(app.bridge.name)   # 'stub' or 'android'

The build pipeline runs twelve independent, individually timed stages:

validate → collect → compile → icons → toolchain → runtime
        → jni → dex → resources → assets → sign → verify

---

UI components

Eight components. All of them accept id, style, visible and enabled.

Label

Static or updatable text.

label = Label("Heading", style=Style(font_size=24, bold=True))
label.set_text("New text")

Button

Button("Save", on_press=self.save)
Button("Unavailable", on_press=self.save, enabled=False)   # taps ignored

TextInput

TextInput(
    placeholder="Your name",
    max_length=50,             # extra characters are trimmed automatically
    on_change=lambda value: print(value),
)

TextInput(password=True)       # masked
TextInput(multiline=True)      # multi-line

on_change fires only on a genuine change — writing the same value again does nothing. While the field has focus the framework never overwrites its contents, so the keyboard stays open and the caret does not jump.

Methods: set_value(text), clear().

Switch

switch = Switch(checked=True, on_toggle=lambda state: print(state))
switch.toggle()            # returns the new state
switch.set_checked(False)

ProgressBar

bar = ProgressBar(40, maximum=100)
bar.set_value(150)         # clamped to maximum
bar.fraction               # 0.0 … 1.0

ProgressBar(indeterminate=True)    # spinner

Image

Image("assets/logo.png", fit="cover")   # contain | cover | fill | none

Paths are relative to your project directory.

Spacer

Spacer(16)     # 16 dp of empty space

Divider

Divider()                       # hairline between sections
Divider(inset=16, thickness=2)

---

Layout

Containers, freely nestable.

Column(a, b, c, spacing=12)                # vertical stack
Row(a, b, spacing=8, align=Align.CENTER)   # horizontal stack
Grid(a, b, c, d, columns=2, spacing=12)    # equal-width cells
ScrollView(content, spacing=8)             # scrollable region
Stack(background, foreground)              # layered, last on top
SafeArea(content)                          # clears the notch and status bar

Grid

The container for cards, galleries and menus. Every cell in a column gets the same width, so two stat cards stay aligned even when one holds 5 and the other 2 h 45 m — which is exactly what Row(weight=1) cannot guarantee.

Grid(
    card("Completed", "12"),  card("Focus time", "5 h"),
    card("Breaks", "4"),      card("Average", "25 m"),
    columns=2,
    spacing=12,                       # or row_spacing= / column_spacing=
)

Rows fill left to right; the last row may be partially filled.

Expanded and Flexible

Share out the space left over on the main axis.

Row(
    Expanded(Button("Start")),            # half
    Expanded(Button("Reset"), flex=2),    # twice as wide
    spacing=8,
)

Expanded makes the child fill its share, Flexible lets it stay smaller.

Divider

Column(
    header,
    Divider(),                                   # hairline
    Divider(inset=16, thickness=2),              # inset, thicker
    Divider(vertical=True),                      # inside a Row
    body,
)

SafeArea

def build(self) -> Widget:
    return SafeArea(Column(...))                 # all edges
    return SafeArea(content, top=False)          # header bleeds upwards

Padding comes from the real window insets, so it is right on every device instead of a hard-coded guess.

Alignment

align positions children along the container's own axis; cross_align positions them across it.

Row(a, b, align=Align.SPACE_BETWEEN, cross_align=Align.CENTER)
Column(a, b, cross_align=Align.STRETCH)

Options: Align.START, Align.CENTER, Align.END, Align.SPACE_BETWEEN, and Align.STRETCH for cross_align.

---

Styling

Style(
    font_size=18,
    bold=True,
    italic=False,
    color=Color.PRIMARY,
    background=Color.SURFACE,
    padding=EdgeInsets.all(16),
    margin=EdgeInsets.symmetric(horizontal=8, vertical=4),
    corner_radius=8,
    elevation=2,
    align=Align.CENTER,
)

Spacing between specific neighbours

spacing on a container applies the same gap everywhere. When one gap must differ, add a margin to the individual widget — the two are added, not replaced:

Column(
    header,
    Label("close to the header"),
    Label("pushed further down", style=Style(margin=EdgeInsets(top=24))),
    spacing=8,          # this one sits 8 + 24 dp below its neighbour
)

Size constraints

Style(min_width=120, max_width=200)     # a card that cannot collapse or sprawl
Style(aspect_ratio=16 / 9)              # keep a shape whatever the width
Style(min_height=44)                    # a comfortable tap target
Style(weight=1)                         # share of a Row/Column (see Expanded)
Style(width=120, height=48)             # a fixed size in dp
Style(width="match")                    # fill the parent ("wrap" also works)
Style(elevation=4)                      # a drop shadow (Android 5+)

Contradictory bounds raise immediately — Style(min_width=200, max_width=120) is a ValueError, not a widget that silently clips to nothing on device.

Built-in colours: PRIMARY, ACCENT, BACKGROUND, SURFACE, TEXT, TEXT_MUTED, SUCCESS, WARNING, ERROR, TRANSPARENT. Custom colours use #RGB, #RRGGBB or #AARRGGBB.

Styles are immutable, so a base style is safe to share:

BASE = Style(font_size=16, color=Color.TEXT)

Label("Normal", style=BASE)
Label("Error", style=BASE.merge(color=Color.ERROR, bold=True))

Invalid values fail fast: Style(color="red") raises ValueError.

EdgeInsets helpers: EdgeInsets.all(8), EdgeInsets.symmetric(horizontal=8, vertical=4), EdgeInsets(left, top, right, bottom).

---

Screens and navigation

A screen builds a widget tree and receives lifecycle callbacks.

class Settings(Screen):
    title = "Settings"

    def build(self) -> Widget:
        return Column(
            Label("Second screen"),
            Button("Back", on_press=lambda: self.app.pop()),
        )

    def on_mount(self):   ...   # once, when pushed onto the stack
    def on_show(self):    ...   # every time it becomes visible
    def on_hide(self):    ...   # when another screen covers it
    def on_unmount(self): ...   # once, when popped

Navigation is a stack:

app.push(Settings())            # on_hide(current) → on_mount → on_show
app.pop()                       # on_hide → on_unmount → on_show(previous)

app.navigator.replace(Other())  # swap the top screen
app.navigator.reset(Home())     # clear the stack, start fresh
app.navigator.depth             # how many screens are stacked
app.screen                      # the visible screen

The root screen is never popped — pop() returns None instead of leaving a blank window. The hardware back button is wired up automatically.

Do not push the same screen object twice; that raises PyMobileError. Create a new instance each time: app.push(Settings()).

Find a widget anywhere in the current screen:

self.find("counter").set_text("5")     # matches Label(..., id="counter")

---

Updating the screen

Change a widget and the screen redraws itself. There is no render() to forget.

class Home(Screen):
    def build(self) -> Widget:
        self.taps = 0
        self.counter = Label("Taps: 0")        # id becomes "counter"
        return Column(self.counter, Button("Tap", on_press=self.on_tap))

    def on_tap(self) -> None:
        self.taps += 1
        self.counter.text = f"Taps: {self.taps}"    # that is the whole update

self.counter.text = ... and self.counter.set_text(...) do the same thing. Every stateful property works this way: text, value, checked, visible and enabled.

Redraws are coalesced, so a handler that updates six widgets still produces a single frame. Assigning a value that has not changed renders nothing at all, and mutating a widget on a screen that is not visible is free.

Group updates explicitly when you build them in a loop:

with app.batch():
    for label, value in zip(self.labels, values):
        label.text = value
# one render happens here

Method	When to use
(nothing)	a property changed — handled for you
self.refresh()	the tree itself changed (rows added or removed)
app.render()	you want a frame pushed out right now

def on_data_loaded(self) -> None:
    self.items = fetch_items()
    self.refresh()          # the number of rows changed

App("Demo", auto_render=False) restores the old manual behaviour; in that mode the first missed redraw logs a warning rather than leaving you guessing.

---

Reacting to events

Subscribe from a screen and the handler is removed when the screen goes away:

class TimerScreen(Screen):
    def on_mount(self) -> None:
        self.on("pomodoro:tick", self.on_tick)   # cancelled on unmount

    def on_tick(self, event) -> None:
        self.clock.text = event.get("remaining")

With app.on() the handler of a popped screen stays subscribed: it keeps firing, keeps the screen alive, and runs twice as soon as the screen is pushed again. self.on() avoids that. To bind a handler registered elsewhere, pass the screen: app.on("tick", handler, screen=self).

---

Notifications

app.notify("Done", "File saved")               # returns a notification id
app.notify("Syncing", "In progress…", ongoing=True)   # cannot be swiped away
app.notifications.cancel(notification_id)

The notification channel is created automatically. On Android 13+ you need the POST_NOTIFICATIONS permission — see below.

---

Vibration

app.vibrate(100)                               # one shot, milliseconds
app.vibration.preset("success")
app.vibration.pattern([0, 100, 50, 100])       # [wait, buzz, wait, buzz]
app.vibration.cancel()

Presets: tick, click, double, success, error, heartbeat.

Pulses shorter than about 50 ms cannot be felt on most hardware, so short values are stretched automatically and waveforms are sent with explicit amplitudes — several devices silently ignore the default.

---

Permissions

from pymobile import Permission

app.permissions.has(Permission.CAMERA)              # bool
app.permissions.request(Permission.CAMERA)          # {'android.permission.CAMERA': True}
app.permissions.missing([Permission.CAMERA, "VIBRATE"])
app.require_permissions(Permission.CAMERA)          # raises PermissionError_ if denied

Three spellings are accepted: "CAMERA", "android.permission.CAMERA" and Permission.CAMERA.

Three rules that save hours

1. Declare every permission in pymobile.toml. Android denies an undeclared permission silently — no dialog appears at all. The compiler warns you when code requests something the manifest lacks:

! requested in code but not declared in pymobile.toml: android.permission.CAMERA
  — Android will deny them without showing a dialog

2. Ask after the first screen is visible. A request issued before the window exists is dropped by the system. Put it in on_show(), not before app.run():

def on_show(self) -> None:
    if self.visits == 1:
        self.app.permissions.request(Permission.CAMERA)

3. Two refusals disable the dialog forever. Android then returns an instant denial. PyMobile detects this and opens the app's settings page with an explanation, instead of failing mutely.

---

HTTP requests

A client built on the standard library — no third-party dependency, so nothing extra lands in the APK.

from pymobile import HttpClient

client = HttpClient(
    base_url="https://api.example.com",
    headers={"Authorization": "Bearer ..."},
    timeout=10,
    retries=2,           # exponential backoff
)

client.get("/items", params={"page": 2})
client.post("/items", json={"name": "Widget"})
client.put("/items/1", json={"name": "Updated"})
client.delete("/items/1")

The response object:

response = client.get("/items")

response.status      # 200
response.ok          # True for 2xx
response.json()      # parsed JSON
response.text        # decoded text
response.content     # raw bytes
response.headers     # lowercase keys
response.elapsed     # seconds

Error statuses are returned, not raised — they are valid HTTP responses:

response = client.get("/missing")
if not response.ok:
    print(response.status)        # 404

response.raise_for_status()       # raises NetworkError for 4xx/5xx

Retries cover connection failures and 408/425/429/5xx.

HTTPS works out of the box: a bundle of root certificates is packaged into the APK, because Android provides no certificate file where OpenSSL looks for one.

Remember to list android.permission.INTERNET in your config.

---

Languages

The device language plus a small catalogue, which is usually all a mobile app needs. gettext and .mo files keep working — the standard library is packaged in full.

from pymobile import t, translations, device_language

translations.load_dir("locales")          # locales/en.json, locales/uk.json …
translations.use(device_language(default="en"))

Label(t("greeting", name="Оксана"))       # "Привіт, Оксана!"

{
  "greeting": "Привіт, {name}!",
  "items": {
    "one":  "{count} елемент",
    "few":  "{count} елементи",
    "many": "{count} елементів"
  }
}

t("items", count=1)     # 1 елемент
t("items", count=3)     # 3 елементи
t("items", count=5)     # 5 елементів

Plural forms cover zero, one, few, many and other, so Slavic rules work, not only the English one. Lookup falls back from pt-br to pt and then to the default language, and a missing key renders as the key itself (logged once) rather than raising in the middle of a screen.

Switching language redraws whatever is on screen — translations.use("uk") is enough, because t() runs inside build() and the screen is rebuilt for you.

device_language() reads the real system setting on Android — including Android 13 per-app language overrides — and the usual environment variables on a desktop. Force one during development with PYMOBILE_LANGUAGE=uk.

Already using xgettext? translations.install_gettext("app", "locale") reads your compiled .mo catalogues instead.

---

Events

A synchronous event bus decouples UI from application logic.

# framework events
app.on("app:start",     lambda e: ...)
app.on("app:stop",      lambda e: ...)
app.on("app:render",    lambda e: ...)
app.on("screen:change", lambda e: print(e.source))

# your own events
app.events.emit("cart:updated", source="CartScreen", count=3)
app.on("cart:updated", lambda e: print(e.get("count")))

subscription = app.on("x", handler)
subscription.cancel()          # always unsubscribe in on_unmount()

An exception inside one handler is logged and never prevents the others from running.

---

Timers

Schedule work without importing threading. Callbacks fire on a background thread on every platform, so the UI never blocks, and the same code runs on desktop and device.

# every second — drive a clock, poll a sensor, tick a game
ticker = app.set_interval(1000, self.on_tick)

# once, after a delay — dismiss a splash, auto-save
app.set_timeout(250, splash.dismiss)

# stop early
ticker.cancel()

Every call returns a TimerHandle with .cancel() and .cancelled. An exception inside a callback is logged and does not stop a repeating timer. All timers are cancelled automatically when the app stops, but you should still cancel a repeating timer in on_unmount() so a popped screen does not keep ticking:

def on_unmount(self) -> None:
    self.ticker.cancel()

Intervals do not drift

Ticks are scheduled against a fixed timeline — tick n is due at start + n × interval — so the time your callback spends working is not added to the next wait. A one-second timer is still on the second an hour later, which matters for clocks, metronomes and games.

app.set_interval(1000, self.tick)                          # aligned (default)
app.set_interval(1000, self.poll, drift_correction=False)  # fixed pause between runs

Deadlines missed while the device was asleep are skipped rather than fired as a burst, so a metronome stays in phase instead of stuttering to catch up. Use drift_correction=False for a poller that must not overlap itself.

---

Configuration reference

Everything lives in pymobile.toml (or a [tool.pymobile] table inside pyproject.toml).

[app]
# --- identity ---
name = "My App"                 # shown under the launcher icon
package = "com.example.myapp"   # reverse-DNS, lowercase segments
version = "1.0.0"
version_code = 1                # integer; must increase for each Play upload

# --- entry point ---
entrypoint = "main.py"
source_dir = "."

# --- Android platform ---
min_sdk = 21                    # Android 5.0
target_sdk = 34                 # Android 14
orientation = "portrait"        # portrait | landscape | sensor | user

# Every permission requested at runtime must be listed here.
permissions = [
    "android.permission.INTERNET",
    "android.permission.VIBRATE",
    "android.permission.POST_NOTIFICATIONS",
]

# --- resources ---
icon = "assets/icon.png"        # optional; default icon used otherwise

# --- build ---
abis = ["arm64-v8a"]
output_dir = "build"
optimize = true                 # ship bytecode instead of sources
strip_debug = true              # -OO: drop docstrings and asserts
exclude = ["tests/**", "**/__pycache__/**"]

Key	Default	Meaning
name	PyMobile App	display name
package	org.pymobile.app	unique application id
version	0.1.0	user-visible version
version_code	1	internal build number
entrypoint	main.py	module to execute
source_dir	.	root of your sources
min_sdk	21	oldest supported Android
target_sdk	34	Android version you target
orientation	portrait	screen orientation
permissions	["…INTERNET"]	manifest permissions
icon	(none)	path to a square PNG
abis	["arm64-v8a"]	architectures
output_dir	build	where the APK is written
optimize	true	package .pyc
strip_debug	true	compile with -OO
exclude	see above	glob patterns to skip

Every value is validated before the build starts, and each error carries a fix:

✗ Invalid package name 'Bad_Package'
  hint: Use reverse-DNS with lowercase segments, e.g. com.example.myapp

Inspect the resolved configuration with pymobile info or pymobile info --json.

---

Building an APK

pymobile build --native                    # incremental
pymobile build --native --clean            # ignore the cache
pymobile build --native -v                 # per-stage timings
pymobile build --native --icon logo.png    # override the icon
pymobile build --native --output dist      # different directory
pymobile build --native --no-optimize      # ship .py for debugging
pymobile build --native --minimal-stdlib   # drop desktop-only stdlib
pymobile build --native --no-ssl           # drop OpenSSL (no HTTPS)

Without --native you get a lightweight structural package used for quick checks. It does not install on a device.

A rebuild with no changes finishes instantly:

✓ up to date: my-app-1.0.0.apk (16.6 MB)

The cache tracks every input: sources, configuration and icon.

Inside the APK:

AndroidManifest.xml          generated from your config
classes.dex                  launcher activity and the view renderer
resources.arsc               compiled resources
lib/arm64-v8a/*.so           CPython, OpenSSL, SQLite, the JNI bridge
assets/app/                  your code and the pymobile package
assets/python/               standard library and CA certificates
res/mipmap-*/icon.png        icons, five densities
META-INF/                    signature (v1+v2+v3)

Builds are reproducible: identical inputs produce a byte-identical APK. The file is written to a temporary path and moved into place, so an interrupted build never leaves a corrupt artifact.

Size

A hello-world APK is 16.6 MB, down from 21.6 MB in 0.2.0. The official CPython Android runtime ships every support library twice — libcrypto.so and libcrypto_python.so are byte-identical, and only the _python names are actually linked — so 5 MB of each APK was the same three libraries repeated. That is fixed for every build; no flag needed.

Two opt-in flags trim further:

Flag	Saves	Cost
--minimal-stdlib	~1.7 MB	no pydoc, unittest, venv, pdb, xmlrpc on device
--no-ssl	~4.7 MB	no HTTPS at all — HttpClient over TLS stops working

With both, the same app is 11.7 MB. --no-ssl only makes sense for an app that talks to nothing, or over plain HTTP on a local network.

21.6 MB   0.2.0
16.6 MB   0.3.0                              duplicate libraries removed
11.7 MB   0.3.0 --minimal-stdlib --no-ssl

---

Application icon

icon = "assets/icon.png"

Provide a square PNG, JPG or WebP — 512×512 works best. It is resized into all five densities (48, 72, 96, 144 and 192 px). Install the icons extra for high-quality resampling:

pip install "py-mobile[icons]"

Without it the icon is copied unscaled; the build still succeeds. With no icon configured, a bundled default is used, so a build never fails over a missing asset.

---

Installing on a phone

Without a cable: copy the .apk to your device through cloud storage or a messenger, open it there and allow installation from unknown sources.

Over USB, with USB debugging enabled:

adb install -r build/my-app-1.0.0.apk

adb lives in ~/.andro/sdk/platform-tools/.

---

Debugging

Everything your app prints, including tracebacks, goes to logcat:

adb logcat -s pymobile pymobile.stdout pymobile.stderr

Tag	Contents
pymobile	framework and renderer messages
pymobile.stdout	your print() output
pymobile.stderr	exceptions and tracebacks

If a single widget fails to render, it is replaced by red text naming the error while the rest of the screen keeps working.

---

Testing your app

StubBridge records every platform call, so no emulator is needed and tests run in milliseconds.

from pymobile import App
from pymobile.core.bridge import StubBridge


def test_button_posts_a_notification():
    bridge = StubBridge(verbose=False)
    app = App("Test", bridge=bridge)
    app.run(Home())

    app.screen.find("btn").press()

    assert bridge.calls_named("notify")
    spec = list(bridge.notifications.values())[0]
    assert spec.title == "Hello"


def test_permission_denial_is_handled():
    denying = StubBridge(grant_permissions=False, verbose=False)
    app = App("Test", bridge=denying)
    assert app.permissions.request("CAMERA") == {"android.permission.CAMERA": False}

Useful members: calls, calls_named(name), notifications, granted, reset(), and the grant_permissions=False constructor flag.

---

Error handling

Every exception derives from PyMobileError and carries a message and an actionable hint.

from pymobile.errors import PyMobileError, NetworkError, ConfigError

try:
    response = client.get("/items")
except NetworkError as error:
    print(error.message)   # what happened
    print(error.hint)      # how to fix it
except PyMobileError:
    ...                    # catch anything from the framework

Exception	Raised when
ConfigError	configuration missing or invalid
NetworkError	request failed, host unreachable, invalid JSON
PermissionError_	the user declined a permission
ResourceError	an icon or template could not be read
BridgeError	a call into Android failed
PlatformError	feature unavailable on this platform

The CLI prints only the message and hint. Add -v for a full traceback.

---

Desktop preview

pymobile preview renders the first screen into a picture right on your laptop — no emulator, no phone. It runs your entry point with the stub bridge and draws the resulting widget tree:

pymobile preview            # text picture in the terminal
pymobile preview --ids      # annotate each widget with its id
pymobile preview --png ui.png   # save a raster image (needs Pillow)

The text picture shows the real layout — Row children sit side by side, ProgressBar is drawn as a filled bar, Switch shows its state:

┌──────────────────────────────┐
│ Pomodoro Focus               │
├──────────────────────────────┤
🎯 Focus
25:00
[░░░░░░░░░░░░░░░░] 0%
(Start)  (Reset)
Vibrate when done  [●] on
└──────────────────────────────┘

The same renderer is importable, so tests and notebooks can snapshot a screen too:

from pymobile.core.ui.preview import render_ascii
print(render_ascii(app.screen.build(), title="Home"))

An interactive window

pymobile run --gui opens a real window instead of printing once. Buttons run their callbacks, switches and text fields feed events back through the same path the phone uses, and navigation works — a back button appears as soon as the stack is deeper than one screen. Toasts and vibration show up in the status strip.

pymobile run --gui

It is built on Tkinter, which ships with CPython, so it costs no dependency. Trees are patched into the existing widgets when the structure has not changed, so typing in a field does not lose focus.

In a browser

pymobile run --web serves the same interactive preview over HTTP, which is what you want on a remote machine, in a container, or when Tk is unavailable:

pymobile run --web                 # http://127.0.0.1:8765
pymobile run --web --port 9000
pymobile run --web --host 0.0.0.0  # open it from your phone on the same Wi-Fi

The page is plain HTML built from the same serialised tree the phone receives, so it cannot drift from the real renderer. Buttons, switches and text fields post back to the app, and the page polls for updates, so a timer tick appears on its own. Widget ids are carried into data-wid attributes, so the browser inspector tells you exactly which widget a node is.

Hot reload

pymobile watch re-renders every time you save:

pymobile watch                  # text picture on every save
pymobile watch --png ui.png     # write an image instead
pymobile watch --interval 0.1   # poll faster

Editing an imported helper module counts too, not just main.py. A syntax error prints the exception and keeps watching, so a half-typed line does not end the session.

• watching /home/me/pomodoro — press Ctrl+C to stop
✓ rendered in 12 ms

• changed: main.py
✓ rendered in 11 ms

---

CLI reference

Command	Description
pymobile init [dir]	create a project (-n name, -p package, -f force)
pymobile setup-sdk	install the Android toolchain (--with-ndk, --path)
pymobile build --native	build a signed, installable APK (--minimal-stdlib, --no-ssl)
pymobile run	run the app on your machine (--gui window, --web browser)
pymobile watch	re-render on every save (--png, --ids, --interval)
pymobile preview	draw the first screen as a picture (--png, --ids)
pymobile info	show the resolved configuration (--json)
pymobile doctor	check environment and project health
pymobile clean	remove build artifacts

Global flags -v (verbose) and -c PATH (project directory) work both before and after the sub-command.

---

Extending the framework

The architecture is designed so that additions never touch existing code.

A new widget — subclass Widget, set type_name, override props(), then add a branch to ViewBuilder.java:

from pymobile.core.ui.widget import Widget


class Slider(Widget):
    type_name = "Slider"
    __slots__ = ("value", "minimum", "maximum")

    def __init__(self, value=0.0, *, minimum=0.0, maximum=100.0, **kwargs):
        super().__init__(**kwargs)
        self.value, self.minimum, self.maximum = value, minimum, maximum

    def props(self):
        return {**super().props(), "value": self.value,
                "minimum": self.minimum, "maximum": self.maximum}

A new Android API — add a method to Bridge, implement it in AndroidBridge and StubBridge, wrap it in a small class under core/api/.

A new build stage — write a method and add one line to BuildPipeline.run(); timing and logging come for free.

A new platform — implement Bridge once; nothing else changes.

---

Limitations

• arm64-v8a only. Covers roughly 99% of active devices; x86_64 is planned.
• APK size is about 16.6 MB (11.7 MB with --minimal-stdlib --no-ssl), dominated by the interpreter and standard library.
• Android 5.0 (API 21) minimum.
• The renderer covers the components documented here; more are being added.

---

FAQ

Why doesn't my UI update? It should: assigning to a widget property redraws the screen by itself. If the structure changed — rows added or removed — call self.refresh() to rebuild through build(). See Updating the screen.

Why does pymobile run show no window? By default it runs your logic through the stub bridge without native views, which is what makes apps testable without an emulator. Use pymobile run --gui for a real, clickable window, pymobile preview for a text picture, or pymobile watch to re-render on every save. See Desktop preview.

Why doesn't a 404 raise an exception? Because it is a valid HTTP response. Use response.ok or response.raise_for_status().

Why is no permission dialog shown? Either the permission is missing from pymobile.toml, or you have already denied it twice and Android has blocked further prompts. See Permissions.

Why doesn't my button respond? Check enabled — a disabled button ignores taps.

Why does push() raise an error? The same screen object cannot be pushed twice. Create a new instance.

Where did my print() output go? To logcat: adb logcat -s pymobile.stdout.

How do I make the APK smaller? Keep optimize = true and strip_debug = true, trim files with exclude, and list a single ABI.

Can I keep the config in pyproject.toml? Yes, under [tool.pymobile]. If both files exist, pymobile.toml wins.

Do I need Android Studio? No. pymobile setup-sdk downloads only the command-line tools it needs.

---

Contributing

git clone https://github.com/Maksum867/py-mobile.git
cd pymobile
pip install -e ".[dev]"

pytest                  # 331 tests
ruff check pymobile     # linting
mypy pymobile           # strict type checking

To rebuild the native artifacts from source (requires pymobile setup-sdk --with-ndk):

PYMOBILE_BUILD_JAVA=1 PYMOBILE_BUILD_JNI=1 pymobile build --native --clean

Issues and pull requests are welcome.

---

Documentation

• GUIDE.md — extended guide with worked examples
• CHANGELOG.md — release history

License

MIT — see LICENSE.