Enforce precision in decimal python

Question

In some environments, exact decimals (numerics, numbers...) are defined with scale and precision, with scale being all significant numbers, and precision being those right of the decimal point. I want to use python's decimal implementation to raise an error, if the precision of the casted string is higher than the one defined by the implementation.

So for example, I have an environment, where scale = 4 and precision = 2. How can I achieve these commands to raise an error, because their precision exceeds that of the implementation?

decimals.Decimal('1234.1')
decimals.Decimal('0.123')

Answer 1

The closest I could find in the decimal module is in the context.create_decimal_from_float example, using the Inexact context trap :

>>> context = Context(prec=5, rounding=ROUND_DOWN)
>>> context.create_decimal_from_float(math.pi)
Decimal('3.1415')
>>> context = Context(prec=5, traps=[Inexact])
>>> context.create_decimal_from_float(math.pi)
Traceback (most recent call last):
    ...
Inexact: None

The decimal module doesn't seem to have the concept of scale. It's precision is basically your scale + your precision.