range-digit is library of decimal digit which has low and sup.
from range_digit import RangeDigit
from decimal import Decimal
d = RangeDigit("1.240")
print(d) # 1.240
print(d - Decimal("1.2")) # 0.040
print(d / 2) # 0.620
print(d.low) # 1.2395
print(d.sup) # 1.2405
print(d.tostr()) # <RangeDigit [1.2395 - 1.2405)>