Python : get child process pid and add to dictionary with parent process id

My application creates a pid file with details of parent pid in it. I have got a task to need to identify all the child pids associated with parent pid and store in dictionary format to a log.

I have written below script, in that i am able to get the parent pid with file name in dictionary. But stuck in a place in getting the the details of child pid in the output.

Python version : 2.6

To get the child process id used below function

def child(pid):
        process = subprocess.Popen(['pgrep','-P', str(pid) ], stdout=subprocess.PIPE,universal_newlines=True)
        output = process.communicate()
        return output

Child returns output in format

('12345','45678', None)

But unsure how to add the returned values to the existing dictionary.

Sample input file

cat file 1 
39007

cat file 2 
39023

Tried Script

def child(pid):
        process = subprocess.Popen(['pgrep','-P', str(pid) ], stdout=subprocess.PIPE,universal_newlines=True)
        output = process.communicate()
        return output


def get_pids(market):
        files=["file1", "file2" ]
        pids={}
        for pid_file in files:
                try:
                        with open(pid_file, 'r') as f:
                                al_pid = f.readline().strip()
                                child(pid)
                                pids[pid_file]=al_pid
                        f.close()
                except:
                        print("Unable to open : " + pid_file + ". Skipping file")

print pids

recieved Output

{'file': '39007','file2': '39023'}

Expected output

{'file': [39007, child_pid1, child_pid2],'file2': [39023, child_pid3, child_pid4]}

I can resolve my problem with the below code.

files=['file','file2']
pids={}

def child(pid):
        process = subprocess.Popen(['pgrep','-P', str(pid) ], stdout=subprocess.PIPE)
        output = process.stdout.readlines()
        out=[p.strip() for p in output]
        return out


for pid_file in files:
                with open(pid_file, 'r') as f:
                        al_pid = f.readline().strip()
                        pid=child(al_pid)
                        pid.insert(0,al_pid)
                        pids[pid_file]=pid
                f.close()
print pids