pythonnative/src/pythonnative/component.py at main · pythonnative/pythonnative · GitHub

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"""The ``@component`` decorator and the [`Component`][pythonnative.Component] type.

A component is a plain Python function that takes props and returns a

[`Node`][pythonnative.element.Node]: an [`Element`][pythonnative.Element],

a list of elements, or ``None``. Decorating it with

[`@component`][pythonnative.component.component] turns it into a

[`Component`][pythonnative.Component]: a callable that *describes* a

render (it returns an ``Element`` whose ``type`` is the component)

instead of performing one. The reconciler invokes the function body

later, with hook state installed.

The decorator preserves the function's signature for type checkers via

:class:`typing.ParamSpec`, so ``Greeting(nme="x")`` is a static error

and editors autocomplete props from the function definition.

Children

--------

Children are positional. A component that accepts children declares a

``*children: pn.Node`` parameter, exactly like the built-in containers:

```python

@pn.component

def Card(*children: pn.Node, title: str = "") -> pn.Node:

return pn.Column(pn.Text(title, style=pn.style(bold=True)), *children)

Card(pn.Text("body"), title="Hello")

```

Positional arguments to a component *without* ``*children`` bind to its

positional parameters, so ``Greeting("World")`` works for

``def Greeting(name: str)``.

Keys

----

``key`` identifies an element, not a prop, so a component's signature

can't declare it. Key a component's element with

[`Element.with_key`][pythonnative.element.Element.with_key], which type-checks

at every call site:

```python

pn.Column(*(Row(item).with_key(item.id) for item in items))

```

Passing ``key=`` to a user component raises ``TypeError``; built-in

factories accept ``key=`` directly.

"""

from __future__ import annotations

import functools

import inspect

from typing import Any, Awaitable, Callable, Dict, Generic, Mapping, Optional, ParamSpec, Union, overload

from . import diagnostics

from .element import Element, Node

__all__ = ["Component", "RenderFn", "component", "memo", "is_component"]

P = ParamSpec("P")

RenderFn = Callable[P, Union[Node, Awaitable[Node]]]

"""A component body: returns a [`Node`][pythonnative.element.Node], or awaits one when ``async def``."""

def _hook_signature(fn: Callable[..., Any]) -> Optional[tuple[str, ...]]:

"""Fast Refresh's hook fingerprint of ``fn``, or ``None`` without the refresh module.

Release bundles omit ``pythonnative.refresh`` (and ship bytecode, which

has no source to fingerprint), so the import is lazy, optional, and

attempted once.

"""

global _refresh_signature

if _refresh_signature is None:

try:

from .refresh import hook_signature

except ImportError:

_refresh_signature = False

else:

_refresh_signature = hook_signature

return _refresh_signature(fn) if callable(_refresh_signature) else None

_refresh_signature: Union[None, bool, Callable[[Callable[..., Any]], Optional[tuple[str, ...]]]] = None

class Component(Generic[P]):

"""A render-function wrapped by [`@component`][pythonnative.component.component].

Calling a ``Component`` does not run the function; it returns an

[`Element`][pythonnative.Element] describing the call so the

reconciler can mount it, preserve its hook state across renders,

and re-run it when its state or props change.

Attributes:

fn: The original render function.

display_name: Name shown in diagnostics and dev tooling

(defaults to ``fn.__name__``).

memoized: Whether [`memo`][pythonnative.memo] was applied, in

which case the reconciler skips re-rendering this component

when its props are shallowly equal to the previous render.

accepts_children: Whether ``fn`` declares ``*children``.

"""

__slots__ = (

"fn",

"display_name",

"memoized",

"props_equal",

"accepts_children",

"_signature",

"_keyed_builtin",

"_is_async",

"refresh_signature",

"__wrapped__",

# ``functools.update_wrapper`` copies ``__module__`` and

# ``__qualname__`` from the render function so Fast Refresh can

# find a component's replacement by module and name; those two

# names can't be slots (they conflict with the class attributes),

# so instances keep a ``__dict__`` for them.

"__dict__",

)

def __init__(self, fn: RenderFn[P], *, display_name: Optional[str] = None, _keyed_builtin: bool = False) -> None:

if isinstance(fn, Component):

raise TypeError(f"{fn!r} is already a component; remove the duplicate @component")

sig = inspect.signature(fn)

accepts_children = False

for name, param in sig.parameters.items():

if param.kind is inspect.Parameter.VAR_POSITIONAL:

accepts_children = True

if name == "key" and not _keyed_builtin:

raise TypeError(

f"{getattr(fn, '__qualname__', fn)!r} declares a 'key' parameter, but 'key' names an element's "

"identity, not a prop. Rename the parameter; key a rendered element with .with_key(...)."

)

self.refresh_signature = _hook_signature(fn)

self.fn = fn

self.display_name: str = display_name or str(getattr(fn, "__name__", "Component"))

self.memoized = False

self.props_equal: Optional[Callable[[Mapping[str, Any], Mapping[str, Any]], bool]] = None

self.accepts_children = accepts_children

self._signature = sig

self._keyed_builtin = _keyed_builtin

self._is_async = inspect.iscoroutinefunction(fn)

self.__wrapped__ = fn

functools.update_wrapper(self, fn, updated=())

# ------------------------------------------------------------------

# Element construction

# ------------------------------------------------------------------

def __call__(self, *args: P.args, **kwargs: P.kwargs) -> Element:

"""Describe a render of this component with the given props."""

key: Optional[str] = None

if "key" in kwargs:

if not self._keyed_builtin:

raise TypeError(

f"{self.display_name}() got key=...; components don't take a key prop. "

f"Use {self.display_name}(...).with_key(key) instead."

)

raw = kwargs.pop("key")

key = None if raw is None else str(raw)

bound = self._signature.bind(*args, **kwargs)

bound.apply_defaults()

children: tuple[Any, ...] = ()

props: Dict[str, Any] = {}

for name, value in bound.arguments.items():

kind = self._signature.parameters[name].kind

if kind is inspect.Parameter.VAR_POSITIONAL:

children = value

else:

props[name] = value

props.pop("key", None)

if diagnostics.is_dev() and not self._keyed_builtin:

from .prop_checks import check_props

check_props(self, props)

return Element(self, props, children, key=key)

# ------------------------------------------------------------------

# Rendering (used by the reconciler)

# ------------------------------------------------------------------

def render(self, element: Element) -> Any:

"""Invoke the render function for ``element``.

Children stored on the element are passed positionally; props

are passed by keyword. Returns whatever the function returned

(an element, a list, ``None``, or a coroutine for ``async def``

bodies).

"""

arguments = dict(element.props)

for name, param in self._signature.parameters.items():

if param.kind is inspect.Parameter.VAR_POSITIONAL:

arguments[name] = element.children

bound = inspect.BoundArguments(self._signature, arguments)

return self.fn(*bound.args, **bound.kwargs)

@property

def is_async(self) -> bool:

"""Whether the render function is an ``async def``."""

return self._is_async

def __repr__(self) -> str:

flags = " memo" if self.memoized else ""

return f"<Component {self.display_name}{flags}>"

def __get__(self, instance: Any, owner: Any = None) -> "Component[P]":

# Components stored on classes (rare) should not bind ``self``.

return self

def component(fn: RenderFn[P]) -> Component[P]:

"""Turn a render function into a [`Component`][pythonnative.Component].

The decorated function may use hooks (``use_state``, ``use_effect``,

etc.) and returns an [`Element`][pythonnative.Element] tree, a list

of elements, or ``None``. Each call site creates an independent

component instance with its own hook state.

Args:

fn: The render function. May be ``async def``; the body is then

driven by the reconciler and suspends on pending awaits (see

[`Suspense`][pythonnative.Suspense]).

Returns:

A ``Component`` whose call signature mirrors ``fn``.

Example:

```python

import pythonnative as pn

@pn.component

def Greeting(name: str = "World"):

return pn.Text(f"Hello, {name}!")

```

"""

return Component(fn)

@overload

def memo(

target: Component[P], *, equal: Optional[Callable[[Mapping[str, Any], Mapping[str, Any]], bool]] = None

) -> Component[P]: ...

@overload

def memo(

target: None = None, *, equal: Optional[Callable[[Mapping[str, Any], Mapping[str, Any]], bool]] = None

) -> Callable[[Component[P]], Component[P]]: ...

def memo(

target: Optional[Component[P]] = None,

equal: Optional[Callable[[Mapping[str, Any], Mapping[str, Any]], bool]] = None,

) -> Any:

"""Skip a component's render when its props haven't changed.

Apply on top of ``@component``. When the reconciler re-renders the

parent tree, a memoized child is skipped (its previously-rendered

subtree is reused) iff its props and children are equal to the

previous render and none of its own state setters fired. Props are

compared shallowly by default: callables by identity, everything

else by ``==``.

Pair with [`use_callback`][pythonnative.use_callback] when passing

callbacks as props, otherwise a fresh closure defeats the memo.

Args:

target: A [`Component`][pythonnative.Component].

equal: Optional custom comparator ``(old_props, new_props) ->

bool`` replacing the shallow comparison.

Returns:

The same component, marked for memoization (or a decorator when

called with keyword arguments only).

Example:

```python

@pn.memo

@pn.component

def ExpensiveRow(label: str):

...

@pn.memo(equal=lambda a, b: a["id"] == b["id"])

@pn.component

def Row(id: int, extra: dict):

...

```

"""

def apply(comp: Component[P]) -> Component[P]:

if not isinstance(comp, Component):

raise TypeError("@memo must wrap a @component; write @memo above @component")

comp.memoized = True

comp.props_equal = equal

return comp

if target is None:

return apply

return apply(target)

def builtin_component(fn: RenderFn[P]) -> Component[P]:

"""Framework-internal ``@component`` whose signature may declare ``key``.

Built-in factories implemented as components (``FlatList``,

``SectionList``) keep a typed ``key=`` parameter like every other

built-in factory. The key becomes the element's identity and never

reaches the render function.

"""

return Component(fn, _keyed_builtin=True)

def is_component(obj: Any) -> bool:

"""Return whether ``obj`` is a [`Component`][pythonnative.Component]."""

return isinstance(obj, Component)

pythonnative/src/pythonnative/component.py at main · pythonnative/pythonnative · GitHub

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