Python, Automation, Problems, Solutions

Let me share, few of the problems that I faced during python automation here,

Handling Passwords across Python and Expect:

Scenario - Login to Hypervisor manager (where VNF is deployed) and reset (power off and on) a particular VM. Meanwhile monitor VNF node for status change. After that VM comes back to service perform assertions for setting test verdict.

Issue: password to VM manager must be captured using python and be sent to expect script as argument. password should not be printed / echoed anywhere. (catch: password may contain special characters)

Solution:
import getpass

pwd = getpass.getpass() # input: my#pwd

=> So password will not be echoed - partly solved

special characters must be escaped before send that as argument to expect script

pwd=re.escape(pwd)

cmd = "expect my_script.exp "+pwd  #expect my_script.exp my\#pwd
os.system(cmd)

=> Fully solved.

The Importance of "exit 0" in shell script:

 Scenario:
Python calls a shell script to kill a process. And based on exit status the Python takes further steps.

Problem:
When the processes that are being killed are interdependent, some time "no such process" error is thrown. So a non-zero exit status is returned to Python and It prints killing NOT successful, eventhough intended killing has been done.

Shell script:

#!/bin/bash

ps -ef | grep xxx | xargs -i kill {}

Python ():

import subprocess

def killme():
  p = subprocess.Popen(['./script.sh'], stdout=subprocess.PIPE)
  out, err = p.communicate()
  if p.returncode !=0:
    print "Killing NOT successful"
  print "Killed"

killme()


Solution:

Added exit 0 in shell script

#!/bin/bash

ps -ef | grep xxx | xargs -i kill {}
exit 0

Using Object of a class as an attribute of another class:

class1.py

class class1:
  def __init__(self):
    self.variable = "One"

class2.py

class class2:
  def __init__(self, obj):
    self.obj = obj

test.py

from class1 import class1
from class2 import class2

c1 = class1()
c2 = class2(c1)
c1.variable = "two"
print c2.obj.variable

#two