How can i access plug variables outside the class in openhtf framework

New to python and openhtf, please help me resolve this.

My Script looks like

class ExamplePlug(plugs.BasePlug):

@conf.inject_positional_args
def __init__(self):
try:
ser = serial.Serial(
#port='dev/ttyUSB0',
port = '/dev/ttyUSB0',
baudrate = 9600,
parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE,
bytesize=serial.EIGHTBITS,
timeout=1, #read timeout
write_timeout=5 #write timeout
)
print ('Connection is open : ',str(ser.isOpen()))
except Exception as e:
print('ERRORRRR..', e)

@htf.plug(serial=ExamplePlug)
@htf.measures(htf.Measurement('value').equals(True))
def testing(test,serial):
packet = 'hello'
ser.write(packet.encode())
test.measurements.value = True

if __name__ == '__main__':
test = htf.Test(testing)
test.add_output_callbacks(
json_factory.OutputToJSON('./{dut_id}.test_result.json',
indent=2))
test.execute(test_start=user_input.prompt_for_test_start())

Earlier this script was working fine, but now it is throwing this error

Error: name 'ser' is not defined

Not sure what is missed here, but according to me this same thing was working perfectly earlier, please suggest something or any alternative to access this ser variable in my testing function.