Python implementation file size conversion

def sizeFormat(size, isDisk=False, precision=2):
    '''
    size format for human.
        byte      ---- (B)
        kilobyte  ---- (KB)
        megabyte  ---- (MB)
        gigabyte  ---- (GB)
        terabyte  ---- (TB)
        petabyte  ---- (PB)
        exabyte   ---- (EB)
        zettabyte ---- (ZB)
        yottabyte ---- (YB)
    '''
    units = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB']
    unit = 1000.0 if isDisk else 1024.0
    if not(isinstance(size, float) or isinstance(size, int)):
        raise TypeError('a float number or an integer number is required!')
    li = [(unit**(i + 1), j) for i,j in enumerate(units)]
    for i in li:
        if size > i[0] and i[1] != li[-1][1]:
            continue
        else:
            return f'{round(size*unit/i[0], precision)}{i[1]}'