This function provides interactive manuals and tutorials.

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)