code: def write_crtf(regions, filename, coordsys='fk5', fmt='.6f', radunit='deg'):
      
  
      output = crtf_objects_to_string(regions, coordsys, fmt, radunit)
      with open(filename, 'w') as fh:
          fh.write(output)
docs: Converts a `list` of `~regions.Region` to CRTF string and write to file.
  
      Parameters
      ----------
      regions : `list`
          List of `~regions.Region` objects
      filename : `str`
          Filename in which the string is to be written. Default is 'new.crtf'
      coordsys : `str`, optional
          Astropy Coordinate system that overrides the coordinate frames of all
          regions. Default is 'fk5'.
      fmt : `str`, optional
          A python string format defining the output precision. Default is .6f,
          which is accurate to 0.0036 arcseconds.
      radunit : `str`, optional
          This denotes the unit of the radius. Default is deg (degrees)
  
      Examples
      --------
      >>> from astropy import units as u
      >>> from astropy.coordinates import SkyCoord
      >>> from regions import CircleSkyRegion, write_crtf
      >>> reg_sky = CircleSkyRegion(SkyCoord(1 * u.deg, 2 * u.deg), 5 * u.deg)
      >>> write_crtf([reg_sky], 'test_write.crtf')
      >>> with open('test_write.crtf') as f:
      ...      print(f.read())
      #CRTF
      global coord=fk5
      +circle[[1.000007deg, 2.000002deg], 5.000000deg]