Python function returns SI order of magnitude and string prefix. Requires numpy.

convOOM.py

def convOOM(x):
    '''Function to return tuple with nearest order of mag along with a
    string prefix in the correct SI units.'''
    assert isinstance(x, float), 'Function expect type float'
    assert (1e-24 < x < 1e27), ('Range must be between 1.0e-24 and 1.0e26: '
                                'Exponent expression might be better choice than SI orders of mag.')
    OOMlist  = ['y', 'z', 'a', 'f', 'p', 'n', 'u', 'm', '', 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y']
    OOMnum = np.log10(x) // 3
    return x * 10 ** (-3 * int(OOMnum)), OOMlist[int(OOMnum + 8)]