B. Точность

from decimal import Decimal, getcontext
from types import TracebackType
from typing import Optional

class Precision:
    old_prec = 3
    new_prec = 3
    def __init__(self, precision: int) -> None:
        try:
            precision = round(precision)
        except Exception:
            raise TypeError
        if precision < 1:
            raise ValueError
        self.old_prec = getcontext().prec
        self.new_prec = precision

    def __enter__(self) -> None:
        #print("call __enter__")
        getcontext().prec = self.new_prec

    def __exit__(self, exc_type, exc_value, exc_tb) -> None:
        #print("call __exit__")
        getcontext().prec = self.old_prec