Memory usage of each processes

#!/usr/bin/python3

import os

os.chdir('/proc/')
collect_pid = []
pname_pid = []
for i in os.listdir():
  if i.isdigit():
    collect_pid += [i]
    for pid in collect_pid:
      try:
        fopen = open('/proc/'+str(pid)+'/status')
        fread = fopen.readlines()[0].strip().lstrip('Name:').lstrip()
        pname_pid += [[int(pid),fread]]
        fopen.close()
      except (PermissionError, FileNotFoundError):
        pass

pname_dict = dict(pname_pid)
pss = []
private_page = []
list_mem = []
for pid_no in sorted(pname_dict.keys()):
  try:
    osmaps = open('/proc/'+str(pid_no)+'/smaps')    
    for text in osmaps.readlines():
      text = text.rstrip()        
      if text.startswith('Pss'):
        pss += [ int(text.lstrip('Pss:').lstrip().rstrip('kB ')) ]          
      if text.startswith('Private'):
        private_page += [ int(text.lstrip ('Private_Clean:').lstrip('Private_Dirty:').lstrip().rstrip('kB ')) ]                       
    Pss = round(sum(pss)/1024)
    Private = round(sum(private_page)/1024)
    Shared = Pss - Private
    Memory_Usage = Private + Shared
    pss = []
    private_page = []
    list_mem += [ [ pid_no,pname_dict.get(pid_no),Private,Shared,Memory_Usage ] ]

  except (PermissionError,FileNotFoundError):
    pass
print("{:>5} {:>9} {:>28} {:>19} {:>21}".format("PID","Process","Private-Memory(MiB)","Shared-Memory(MiB)","Meomory-Usage(MiB)")) 
for pid,comm,prim,shm,memu in list(reversed(sorted(list_mem,key = lambda x: x[4]))):
  print("{:6d}  {:<15}  {:>9}  {:>17}  {:>22}".format(pid,comm,prim,shm,memu))