python - why I cannot import the class in SimPy -

learning simpy right now. using first example code, link https://simpy.readthedocs.org/en/latest/topical_guides/process_interaction.html

this part of code written in interactive mode. want put class ev individual python file named ev.py (shown below).

ev.py

class ev:         def __init__(self, env):             self.env = env             self.drive_proc = env.process(self.drive(env))             self.bat_ctrl_proc = env.process(self.bat_ctrl(env))             self.bat_ctrl_reactivate = env.event()          def drive(self, env):             while true:                 # drive 20-40 min                 yield env.timeout(randint(20, 40))                  # park 1–6 hours                 print('start parking at', env.now)                 self.bat_ctrl_reactivate.succeed()  # "reactivate"                 self.bat_ctrl_reactivate = env.event()                 yield env.timeout(randint(60, 360))                 print('stop parking at', env.now)          def bat_ctrl(self, env):             while true:                 print('bat. ctrl. passivating at', env.now)                 yield self.bat_ctrl_reactivate  # "passivate"                 print('bat. ctrl. reactivated at', env.now)                  # intelligent charging behavior here …                 yield env.timeout(randint(30, 90))  

then import file. run this:

from random import seed, randint seed(23) import simpy import ev env=simpy.environment() ev = ev.ev(env) env.run(until=150) 

when comes step: ev=ev.ev(env), shows there error:

traceback (most recent call last):

file "stdin", line 1, in module

typeerror: constructor takes no arguments