for loop inside a string

Question

I'm trying to write a script in python to make my job easier. I need to use os.system to call some functions to an external software.

Is there a way to insert a for loop inside this string, without having to write obs_dir[n] every time??

import os
obs_dir = ['18185','18186','18187','19926','19987','19994','19995','20045','20046','20081']
xid = ['src21']
i=0

os.system("pset combine_spectra src_arfs=/"
          + obs_dir[0] + "/" + xid[i] + "_" + obs_dir[0] + "_spectrum.arf,"
          + "/" + obs_dir[1] + "/" + xid[i] + "_" + obs_dir[1] + "_spectrum.arf,"
          + "/" + obs_dir[2] + "/" + xid[i] + "_" + obs_dir[2] + "_spectrum.arf,"
          + "/" + obs_dir[3] + "/" + xid[i] + "_" + obs_dir[3] + "_spectrum.arf,"
          + "/" + obs_dir[4] + "/" + xid[i] + "_" + obs_dir[4] + "_spectrum.arf,"
          + "/" + obs_dir[5] + "/" + xid[i] + "_" + obs_dir[5] + "_spectrum.arf,"
          + "/" + obs_dir[6] + "/" + xid[i] + "_" + obs_dir[6] + "_spectrum.arf,"
          + "/" + obs_dir[7] + "/" + xid[i] + "_" + obs_dir[7] + "_spectrum.arf,"
          + "/" + obs_dir[8] + "/" + xid[i] + "_" + obs_dir[8] + "_spectrum.arf,"
          + "/" + obs_dir[9] + "/" + xid[i] + "_" + obs_dir[9] + "_spectrum.arf")

insert a for loop inside this string... You mean a loop around the string — B001ᛦ
– B001ᛦ, Commented Feb 23, 2018 at 11:02

Rakesh · Accepted Answer · 2018-02-23 11:12:45Z

3

You can create the required command by first iterating over the list(obs_dir) and forming the string.

Ex:

import os
obs_dir = ['18185','18186','18187','19926','19987','19994','19995','20045','20046','20081']
xid = ['src21']


s = "pset combine_spectra src_arfs="
for i in obs_dir:
    s += "/{0}/{1}_{0}_spectrum.arf, ".format(i, xid[0])

s = s.strip().rstrip(',')
print s
#os.system(s)

edited Feb 23, 2018 at 11:12

answered Feb 23, 2018 at 11:06

Rakesh

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Comments

Lareb Khalil Syed · Accepted Answer · 2018-02-23 11:08:24Z

2

I think this might be what you want

import os
obs_dir = ['18185','18186','18187','19926','19987','19994','19995','20045','20046','20081']
xid = ['src21']

str_cmd = "pset combine_spectra src_arfs=" + obs_dir[0]
separator = ""
for dir in obs_dir
  str_cmd + =  separator + "/" + dir + "/" + xid[i] + "_" + dir + "_spectrum.arf"
  separator = ","
  
os.system(str_cmd)

answered Feb 23, 2018 at 11:08

Lareb Khalil Syed

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Comments

doctorlove · Accepted Answer · 2018-02-23 11:18:46Z

You have xid[i], but no i, so using xid[0],

"/{}/{}_{}_spectrum.arf".format(obs_dir[1],xid[0],obs_dir[1])

gives

'/18186/src21_18186_spectrum.arf'

So, format helps. Also, join will help join these into a comma separated string:

",".join(['a', 'b'])

gives

'a,b'

Joining this together you get

s = ",".join(["/{}/{}_{}_spectrum.arf".format(o,xid[0],o) for o in obs_dir])

giving the parameter(s) you want

'/18185/src21_18185_spectrum.arf,/18186/src21_18186_spectrum.arf,/18187/src21_18g187_spectrum.arf,/19926/src21_19926_spectrum.arf,/19987/src21_19987_spectrum.arfg,/19994/src21_19994_spectrum.arf,/19995/src21_19995_spectrum.arf,/20045/src21_20g045_spectrum.arf,/20046/src21_20046_spectrum.arf,/20081/src21_20081_spectrum.arfg'

without a spare ',' on the end.

Then use it

os.system("pset combine_spectra src_arfs=" + s)

Yann Vernier · Accepted Answer · 2018-02-23 11:16:59Z

1

Not in the string, but we can build the string using features like list comprehension (in this case, a generator expression) and string joining:

obs_dir = ['18185','18186','18187','19926','19987','19994','19995','20045','20046','20081']
xid = ['src21']
i = 0

print("pset combine_spectra src_arfs=" +
    ",".join("/{0}/{1}_{0}_spectrum.arf".format(n,xid[i])
             for n in obs_dir))

answered Feb 23, 2018 at 11:16

Yann Vernier

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