How to check the size of a float in python?

Question

I want to check whether a float is actually 32 or 64bits (and the number of bits of a numpy float array). There should be a built-in, but just didn\'t find out...

Answer 1

numpy.finfo lists sizes and other attributes of float32 ..., including
nexp : number of bits in the exponent including its sign and bias.
nmant : number of bits in the mantissa.
On a machine with IEEE-754 standard floating point,

import numpy as np
for f in (np.float32, np.float64, float):
    finfo = np.finfo(f)
    print finfo.dtype, finfo.nexp, finfo.nmant

will print e.g.

float32 8 23
float64 11 52
float64 11 52

(Try float16 and float128 too.)