code: def fetch_vega_spectrum(data_home=None, download_if_missing=True):
      """Loader for Vega reference spectrum
  
      Parameters
      ----------
      fname : str
          filter name: must be one of 'ugriz'
      data_home : optional, default=None
          Specify another download and cache folder for the datasets. By default
          all astroML data is stored in '~/astroML_data'.
  
      download_if_missing : optional, default=True
          If False, raise a IOError if the data is not locally available
          instead of trying to download the data from the source site.
  
      Returns
      -------
      data : ndarray
          data[0] is the array of wavelength in angstroms
          data[1] is the array of fluxes in Jy (F_nu, not F_lambda)
      """
      data_home = get_data_home(data_home)
  
      archive_name = os.path.join(data_home, VEGA_URL.split("/")[-1])
  
      if not os.path.exists(archive_name):
          if not download_if_missing:
              raise IOError(
                  "data not present on disk. "
                  "set download_if_missing=True to download"
              )
  
          print("downnloading from %s" % VEGA_URL)
          F = urlopen(VEGA_URL)
          open(archive_name, "wb").write(F.read())
  
      F = open(archive_name, "r")
  
      return np.loadtxt(F, unpack=True)
  
imports: import os
  import numpy
  from urllib.request import urlopen
  from astroML.datasets import get_data_home
label_desc: Use image node_id 2 for calling a global function with example usage: fetch_vega_spectrum(data_home, download_if_missing) and returns: np