NIST Database webscraping

The script allows you to download spectral data for a selected element from: https://physics.nist.gov/PhysRefData/ASD/lines_form.html
Help:

python NIST_lines.py --help

Positional arguments:

positional arguments:
  element               Name of element from NIST Database
  line                  Value of wavelength to be searched
  n                     Number of wavelengths to be searched
  filename              Name of the file with output

Optional arguments:

options:
  -h, --help            show this help message and exit
  --low_w LOW_W         Minimum wavelength value
  --upper_w UPPER_W     Maximum wavelength value
  --sp_num SP_NUM [SP_NUM ...]  List of ionization stages
  --threshold THRESHOLD Intensity threshold

Examples:

python NIST_lines.py Ar 811 10 data 

Output in file data.csv:

	element	sp_num	obs_wl_air(nm)	unc_obs_wl	ritz_wl_air(nm)	unc_ritz_wl	intens	gA(s^-1)	Acc	Ei(cm-1)	Ek(cm-1)	conf_i	term_i	J_i	conf_k	term_k	J_k	Type	tp_ref	line_ref
0	Ar	1	811.531	0.001	811.531	0.001	35000	2.3e+08	B	93143.8	105463	3s2.3p5.(2P*<3/2>).4s	2[3/2]*	2	3s2.3p5.(2P*<3/2>).4p	2[5/2]	3	nan	T5223	L2634
1	Ar	1	810.369	0.001	810.369	0.001	20000	7.5e+07	B+	93750.6	106087	3s2.3p5.(2P*<3/2>).4s	2[3/2]*	1	3s2.3p5.(2P*<3/2>).4p	2[3/2]	1	nan	T5223	L2634
2	Ar	2	810.369	2e-05	810.369	4e-05	12023	nan	nan	143371	155708	3s2.3p4.(3P).3d	4F	3/2	3s2.3p4.(3P).4p	4P*	1/2	nan	nan	L11520
3	Ar	1	805.331	0.001	805.331	0.001	7	2.6e+06	C	106238	118651	3s2.3p5.(2P*<3/2>).4p	2[3/2]	2	3s2.3p5.(2P*<3/2>).4d	2[1/2]*	1	nan	T1218n	L2634
4	Ar	2	804.376	0.002	804.375	2.6e-05	5	nan	nan	148620	161049	3s2.3p4.(1D).4s	2D	3/2	3s2.3p4.(3P).4p	4S*	3/2	nan	nan	L14821
5	Ar	2	816.54	0.0008	816.539	2.7e-05	3	nan	nan	143108	155351	3s2.3p4.(3P).3d	4F	5/2	3s2.3p4.(3P).4p	4P*	3/2	nan	nan	L14821
6	Ar	2	804.431	0.0008	804.43	2.6e-05	2	nan	nan	183676	196103	3s2.3p4.(3P).4d	4D	7/2	3s2.3p4.(3P<1>).4f	2[4]*	9/2	nan	nan	L14821
7	Ar	2	811.065	0.002	811.066	2.7e-05	1	nan	nan	142717	155043	3s2.3p4.(3P).3d	4F	7/2	3s2.3p4.(3P).4p	4P*	5/2	nan	nan	L14821
8	Ar	2	808.375	0.002	808.376	0.00014	1	nan	nan	192712	205079	3s2.3p4.(3P).4d	2D	3/2	3s2.3p4.(3P<2>).5f	2[2]*	5/2	nan	nan	L14821
9	Ar	2	815.065	0.0008	815.065	0.00013	1	nan	nan	192712	204978	3s2.3p4.(3P).4d	2D	3/2	3s2.3p4.(3P<2>).5f	2[3]*	5/2	nan	nan	L14821