How to perform precise calculations in Python, reg

问题:

I need to make computations in the highest possible precision, regardless if the arguments passed are integers, floats or whatever numbers. One way I can think of this is:

import numpy as np
def foo(x, y, z)
a = (np.float64)0
a = x + y * z

I can see a couple of problems with this: 1) I think I need to convert the inputs, not the result for this to work 2)looks ugly (the first operation is a superfluous C-style declaration).

How can I pythonically perform all calculations in the highest available precision, and then store the results in the highest available precision (which is IMO numpy.float64)?

回答1:

To me the obvious answer is Decimal, unless the function needs to be very fast.

import decimal
# set the precision to double that of float64.. or whatever you want.
decimal.setcontext(decimal.Context(prec=34))
def foo(x, y, z)
    x,y,z = [decimal.Decimal(v) for v in (x,y,z)] 
    a = x + y * z
    return a  # you forgot this line in the original code.

If you want a conventional 64bit float, you can just convert the return value to that: return float(a)

回答2:

You can declare variable but You can try to force it to be expected type

import numpy as np
def foo(*args):
    x, y, z = map(np.longdouble, args)
    return x + y * z

foo(0.000001,0.000001, 0.00000000001)