How to get largest possible precision? (Python - Decimal)

Question

I'm using the Decimal class for operations that requires precision.

I would like to use 'largest possible' precision. With this, I mean as precise as the system on which the program runs can handle.

To set a certain precision it's simple:

import decimal
decimal.getcontext().prec = 123 #123 decimal precision

I tried to figure out the maximum precision the 'Decimal' class can compute:

print(decimal.MAX_PREC)
>> 999999999999999999

So I tried to set the precision to the maximum precision (knowing it probably won't work..):

decimal.getcontext().prec = decimal.MAX_PREC

But, of course, this throws a Memory Error (on division)

So my question is: How do I figure out the maximum precision the current system can handle?

Extra info:

import sys
print(sys.maxsize)
>> 9223372036854775807

Answer 1

Trying to do this is a mistake. Throwing more precision at a problem is a tempting trap for newcomers to floating-point, but it's not that useful, especially to this extreme.

Your operations wouldn't actually require the "largest possible" precision even if that was a well-defined notion. Either they require exact arithmetic, in which case decimal.Decimal is the wrong tool entirely and you should look into something like fractions.Fraction or symbolic computation, or they don't require that much precision, and you should determine how much precision you actually need and use that.

If you still want to throw all the precision you can at your problem, then how much precision that actually is will depend on what kind of math you're doing, and how many absurdly precise numbers you're attempting to store in memory at once. This can be determined by analyzing your program and the memory requirements of Decimal objects, or you can instead take the precision as a parameter and binary search for the largest precision that doesn't cause a crash.