Module rowsmyth.lazy

Explicit deferred column values.

View Source

"""Explicit deferred column values."""

from __future__ import annotations

from typing import TYPE_CHECKING, Any

from rowsmyth.errors import LazyValueError

if TYPE_CHECKING:

    from collections.abc import Callable

    from rowsmyth.dataset import RowCtx

class Lazy:

    """

    A column value computed per row from the row context.

    Wrap a callable with :func:`lazy` instead of passing it directly: rowsmyth

    never calls a bare callable, so a class, builtin or partial passed as a

    column value is treated as data rather than silently invoked.

    """

    __slots__ = ("fn",)

    def __init__(self, fn: Callable[[RowCtx], Any]) -> None:

        if not callable(fn):

            msg = f"lazy() requires a callable taking the row context, got {fn!r}"

            raise LazyValueError(msg)

        self.fn = fn

def lazy(fn: Callable[[RowCtx], Any]) -> Lazy:

    """

    Mark a callable as a deferred column value.

    The callable receives the :class:`~rowsmyth.dataset.RowCtx` for the row

    being generated and its return value becomes the column value.

    """

    return Lazy(fn)

Variables

TYPE_CHECKING

Functions

lazy

def lazy(
    fn: 'Callable[[RowCtx], Any]'
) -> 'Lazy'

Mark a callable as a deferred column value.

The callable receives the :class:~rowsmyth.dataset.RowCtx for the row being generated and its return value becomes the column value.

View Source

def lazy(fn: Callable[[RowCtx], Any]) -> Lazy:

    """

    Mark a callable as a deferred column value.

    The callable receives the :class:`~rowsmyth.dataset.RowCtx` for the row

    being generated and its return value becomes the column value.

    """

    return Lazy(fn)

Classes

Lazy

class Lazy(
    fn: 'Callable[[RowCtx], Any]'
)

A column value computed per row from the row context.

Wrap a callable with :func:lazy instead of passing it directly: rowsmyth never calls a bare callable, so a class, builtin or partial passed as a column value is treated as data rather than silently invoked.

View Source

class Lazy:

    """

    A column value computed per row from the row context.

    Wrap a callable with :func:`lazy` instead of passing it directly: rowsmyth

    never calls a bare callable, so a class, builtin or partial passed as a

    column value is treated as data rather than silently invoked.

    """

    __slots__ = ("fn",)

    def __init__(self, fn: Callable[[RowCtx], Any]) -> None:

        if not callable(fn):

            msg = f"lazy() requires a callable taking the row context, got {fn!r}"

            raise LazyValueError(msg)

        self.fn = fn

---

Instance variables

fn