Human: pass a string into subprocess.Popen Assistant: 
Here is some code to set the stdin of the process 'grep f' to be b'one\ntwo\nthree\nfour\nfive\nsix\n'

p = Popen(['grep', 'f'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)
grep_stdout = p.communicate(input='one\ntwo\nthree\nfour\nfive\nsix\n')[0]

#Warning: this code generation is experimental. Please inspect the code for any bugs before executing.