text: 
  '''
  .. module:: skrf.data
  ========================================
  io (:mod:`skrf.data`)
  ========================================
  
  
  This Package provides data to be used in examples and testcases
  
  Modules
  ----------
  .. toctree::
     :maxdepth: 1
  
  
  '''
  import os
  import six
  
  from ..network import Network
  from ..io.general import read
  
  pwd = os.path.dirname(os.path.abspath(__file__))
  
  ntwk1 = Network(os.path.join(pwd, 'ntwk1.s2p'))
  line = Network(os.path.join(pwd, 'line.s2p'))
  ring_slot = Network(os.path.join(pwd, 'ring slot.s2p'))
  tee = Network(os.path.join(pwd, 'tee.s3p'))
  ring_slot_meas = Network(os.path.join(pwd, 'ring slot measured.s1p'))
  '''
  The following networks have been saved using Python2 Pickler. 
  Numpy arrays pickled in Python2 can't be reopenned using Python3, 
  as a consequence (?) of the utf8 support in Python3.
  So the following lines shall only work with Python2.  
  '''
  if six.PY2:
      wr2p2_line = Network(os.path.join(pwd, 'wr2p2,line.ntwk'))
      wr2p2_line1 = Network(os.path.join(pwd, 'wr2p2,line1.ntwk'))
      wr2p2_delayshort = Network(os.path.join(pwd, 'wr2p2,delayshort.ntwk'))
      wr2p2_short = Network(os.path.join(pwd, 'wr2p2,short.ntwk'))
      wr1p5_line = Network(os.path.join(pwd, 'wr1p5,line.ntwk'))
      wr1p5_short = Network(os.path.join(pwd, 'wr1p5,short.ntwk'))
      
      one_port_cal = read(os.path.join(pwd, 'one_port.cal'))
  
  mpl_rc_fname = os.path.join(pwd, 'skrf.mplstyle')
  
  ## material database (taken from wikipedia)
  materials = {
      'copper':{
          'resistivity(ohm*m)':1.68e-8,
          },
      'aluminum':{
          'resistivity(ohm*m)':2.82e-8,
          },
      'gold':{
          'resistivity(ohm*m)':2.44e-8,
          },
      'lead':{
          'resistivity(ohm*m)':1/4.56e6, # from pozar appendix F
          },
      'steel(stainless)':{
          'resistivity(ohm*m)':1/1.1e6, # from pozar appendix F
          },
      'mylar':{
          'relative permativity':3.1,
          'loss tangent':500e-4,
          },
      'quartz':{
          'relative permativity':3.8,
          'loss tangent':1.5e-4,
          },
      'silicon':{
          'relative permativity':11.68,
          'loss tangent':8e-4,
          },
      'teflon':{
          'relative permativity':2.1,
          'loss tangent':5e-4,
          },
      'duroid 5880':{
          'relative permativity':2.25,
          'loss tangent':40e-4,
          },
  
      }
  for k1,k2 in [
      ('cu', 'copper'),
      ('al', 'aluminum'),
      ('au', 'gold')]:
      materials[k1] = materials[k2]
  