[system call and capture STDOUT]

system_call_capture_stdout.py

#! /usr/bin/python3

from subprocess import Popen,PIPE,STDOUT

pmidString=''

command='/home/glwinsor/edirect/efetch -db pubmed -id 153904'

#captures STDOUT without having to use a redirect to a filename
#note that it captures bytes, not a string. Therefore need to specify universtal_newlines=True in order to retain newlines
p = Popen(command, shell=True, stdin=PIPE, stdout=PIPE, stderr=STDOUT,universal_newlines=True)
output = p.stdout.read()

# now write the contents of output to filename.txt    
f = open('filename.txt', 'w')
f.write(str(output))
f.close()