Python: call piped commands using subprocess

For example, I want to call external command:

cat /tmp/fruits.txt | grep apple

, depending on if the input is trusted or not, we have the following two options:

• For untrusted input:

  import subprocess
  
  cat = subprocess.popen(['/bin/cat', '/tmp/fruits.txt'], stdout=PIPE)
  grep = subprocess.popen(['/bin/grep', 'apple'], stdin=cat.stdout, stdout=PIPE)
  cat.stdout.close()
  output = grep.communicate()[0]
  print output
  
  

• For trusted input, you can simply set shell=True:

  import subprocess
  
  output=subprocess.check_output('cat /tmp/fruits.txt | grep apple', shell=True)
  print output