docs: def getHelp(arg=None):
      """
      This function provides interactive manuals and tutorials.
      """
      if arg==None:
          print('--------------------------------------------------------------')
          print('Hello, this is an interactive help system of HITRANonline API.')
          print('--------------------------------------------------------------')
          print('Run getHelp(.) with one of the following arguments:')
          print('    tutorial  -  interactive tutorials on HAPI')
          print('    units     -  units used in calculations')
          print('    index     -  index of available HAPI functions')
      elif arg=='tutorial':
          print('-----------------------------------')
          print('This is a tutorial section of help.')
          print('-----------------------------------')
          print('Please choose the subject of tutorial:')
          print('    data      -  downloading the data and working with it')
          print('    spectra   -  calculating spectral functions')
          print('    plotting  -  visualizing data with matplotlib')
          print('    python    -  Python quick start guide')
      elif arg=='python':
          print_python_tutorial()
      elif arg=='data':
          print_data_tutorial()
      elif arg=='spectra':
          print_spectra_tutorial()
      elif arg=='plotting':
          print_plotting_tutorial()
      elif arg=='index':
          print('------------------------------')
          print('FETCHING DATA:')
          print('------------------------------')
          print('  fetch')
          print('  fetch_by_ids')
          print('')
          print('------------------------------')
          print('WORKING WITH DATA:')
          print('------------------------------')
          print('  db_begin')
          print('  db_commit')
          print('  tableList')
          print('  describe')
          print('  select')
          print('  sort')
          print('  extractColumns')
          print('  getColumn')
          print('  getColumns')
          print('  dropTable')
          print('')
          print('------------------------------')
          print('CALCULATING SPECTRA:')
          print('------------------------------')
          print('  profiles')
          print('  partitionSum')
          print('  absorptionCoefficient_HT')
          print('  absorptionCoefficient_Voigt')
          print('  absorptionCoefficient_SDVoigt')
          print('  absorptionCoefficient_Lorentz')
          print('  absorptionCoefficient_Doppler')
          print('  transmittanceSpectrum')
          print('  absorptionSpectrum')
          print('  radianceSpectrum')
          print('')
          print('------------------------------')
          print('CONVOLVING SPECTRA:')
          print('------------------------------')
          print('  convolveSpectrum')
          print('  slit_functions')
          print('')
          print('------------------------------')
          print('INFO ON ISOTOPOLOGUES:')
          print('------------------------------')
          print('  ISO_ID')
          print('  abundance')
          print('  molecularMass')
          print('  moleculeName')
          print('  isotopologueName')
          print('')
          print('------------------------------')
          print('MISCELLANEOUS:')
          print('------------------------------')
          print('  getStickXY')
          print('  read_hotw')
      elif arg == ISO:
          print_iso()
      elif arg == ISO_ID:
          print_iso_id()
      elif arg == profiles:
          print_profiles()
      elif arg == slit_functions:
          print_slit_functions()
      else:
         help(arg)