Unround decimal numbers.

unround.py

"""
Reconstructs the numerator of a rounded rational number.

All fractions p/q are uniquely identifiable iff abs(q) <= 10**d.

Args:
    x (float): Rounded decimal value.
    d (int): Maximum decimal places used in rounding.
    q (int): Denominator of the fraction.
    r (callable, optional): Rounding function (default is round).

Returns:
    int: The reconstructed numerator if an exact match is found.
    bool: False if no exact match is found.

Examples:
    unround(0.33, 2, 3)/3  # -> 0.3333333333333333
    unround(round(4/11, 1), 1, 11)  # -> 4
    unround(round(5/11, 1), 1, 11)  # -> False
"""
# ~-n is n-1 and -~n is n+1
unround=lambda x,d,q,r=round:r(~-(p:=r(q*x))/q,d)!=r(p/q,d)!=r(-~p/q,d)and p