Shared via mypy Playground

main.py

import builtins
from collections.abc import Callable
from typing import Any, Generic, TypeVar, overload

T = TypeVar('T')

def indent(s: str, spaces: int | str = 4) -> str:
    if isinstance(spaces, int):
        spaces = ' ' * spaces
    return ''.join(spaces+line for line in s.splitlines(True))

class _LogWrapper(Generic[T]):
    """Wraps an object with arbitrary str and/or repr conversions.

    Intended for logging, to ensure that expensive string-ifying operations are only
    performed when log messages are actually generated, and are not performed otherwise.

    Example:
    
    .. code-block::
    
        import numpy as np
        data = np.arange(100).reshape((10, 10))

        import logging
        logger = logging.getLogger('my.logger')
        logger.debug('This is the data: %r', _LogWrapper(data, repr=lambda o: indent(repr(o), 2)))
    """
    obj: T
    repr: Callable[[T], builtins.str]
    str: Callable[[T], builtins.str]

    @overload
    def __init__(
        self: _LogWrapper[None],
        obj: None = ...,
        *,
        repr: Callable[[None], builtins.str] = ...,
        str: Callable[[None], builtins.str] = ...,
    ) -> None: ...

    @overload
    def __init__(
        self: _LogWrapper[T],
        obj: T = ...,
        *,
        repr: Callable[[T], builtins.str] = ...,
        str: Callable[[T], builtins.str] = ...,
    ) -> None: ...

    def __init__(
        self: _LogWrapper[T] | _LogWrapper[None],
        obj: T | None = None,
        *,
        repr: Callable[[T], builtins.str] | Callable[[None], builtins.str] = builtins.str,
        str: Callable[[T], builtins.str] | Callable[[None], builtins.str] = builtins.str,
    ) -> None:
        self.obj = obj
        self.repr = repr
        self.str = str

    def __repr__(self) -> builtins.str:
        return self.repr(self.obj)

    def __str__(self) -> builtins.str:
        return self.str(self.obj)


import logging
import json
logger = logging.getLogger('my.logger')
x = [list(range(i*10, i*10 + 10)) for i in range(10)]
logger.debug(
    'This is the data: %r',
    _LogWrapper(x, repr=lambda o: indent(json.dumps(o, indent=2), 2))
)

reveal_type(
    _LogWrapper(str=lambda o: '< ... there is nothing here ... >')
)

reveal_type(
    _LogWrapper(x, repr=lambda o: indent(json.dumps(o, indent=2), 2))
)