Python对象.__ new __（）在main（）中不接受任何参数

Question

I try to execute some python code but i face a problem with passing the parameters. My python code is the following:

#!/usr/bin/python
import MySQLdb

class Sim(object):

    def print_db_parameters(self):
         print "Host = %s" %self.host
         print "User = %s" %self.user
         print "Password = %s" %self.password
         print "Database = %s" %self.database

def main():
    host = "localhost"
    user = "root"
    password = "root"
    database = "sim"
    sim_test = Sim(host,user,password,database)
    sim_test.print_db_parameters()

if __name__ == "__main__":
    main()   

When i run it, i receive the following error:

Traceback (most recent call last):
  File "Sim.py", line 21, in <module>
    main()   
  File "Sim.py", line 17, in main
    sim_test = Sim(host,user,password,database)
  TypeError: object.__new__() takes no parameters

Do you have any idea?

Answer 1

You don't have an __init__ method for your class, but you're passing parameters to the constructor. You should create an __init__ method that accepts parameters.

Answer 2

You are passing parameters to a class constructor

sim_test = Sim(host,user,password,database)

But not accepting them. You must create an __init__ method to deal with them.

#!/usr/bin/python
import MySQLdb

class Sim(object):
    def __init__(self, host, user, password, database):  #New method!!
        self.host = host
        self.user = user
        self.password = password
        self.database = database

    def print_db_parameters(self):
         print "Host = %s" %self.host
         print "User = %s" %self.user
         print "Password = %s" %self.password
         print "Database = %s" %self.database

def main():
    host = "localhost"
    user = "root"
    password = "root"
    database = "ARISTEIA_vax"
    sim_test = Sim(host,user,password,database)
    sim_test.print_db_parameters()

if __name__ == "__main__":
    main()   

Answer 3

to follow up mipadi with example: It would probably be very helpful to read some tutorials on object oriented programming in python http://docs.python.org/2/tutorial/classes.html

class Sim(object):

    def __init__(self, host, user, password, database):
       self.host = host
       self.user = user
       self.password = password
       self.database = database

    def print_db_parameters(self):
         print "Host = %s" %self.host
         print "User = %s" %self.user
         print "Password = %s" %self.password
         print "Database = %s" %self.database