程序相互交互的多个实例化（Python2.7和Tkinter）

Question

I currently have a restaurant simulation program, GUI by Tkinter and I was finding a way to allow multiple instantiation of the programs to interact with one another in the sense of updating its key variables. (Sorry for my poor English)

Let's say:

• Five Users have opened this program at the same time using same PC. (Hypothetical)
• There are three functions in the program, namely Order , See Inventory ,and See Sales
• Assume that all five have made an order

Now, the restaurant must keep track of the orders made, and the inventory to cook the food.

I tried coding the program by using txt file import and export to keep track of the data but it was just now that I realized the txt file can be edited by programs ONE AT THE TIME. (Cannot edit single txt file at once)

Q: What is the better approach in saving the values of the variables used in the program so that multiple users can use the program with real-time updated values of the variables?

• Someone told me that I could try using Global variables. But how could I possible assign values to them and keep them updated? (Local variables get initialized everytime when the program ran)

Thank you for reading my Question!

Answer 1

You could use the sqlite3 module to create a light-weight database. This does not need a server program; the database manager is in the Python standard library. Multiple instances would read/write to the same file database and sqlite would take care of ensuring consistency.

However, please note that there is a 5-second global lock on most sqlite implementations , so any of your multiple instances must complete its read/write in less than that time or it will cause a 'database locked' exception in the other instances.

Here you have an example:

import sqlite3 as lite
import time


con = lite.connect('common.db')
cur = con.cursor()
cur.execute(
    "CREATE TABLE IF NOT EXISTS restaurant (orderId INT primary key, inventory TEXT, sales INT);")

for i in range(5):
    print "About to insert on ID: %s" % i
    cur.execute("INSERT INTO restaurant VALUES(%d, 'burger', 1)" % i)
    time.sleep(1)

con.close()

If you execute this code on two terminals at the same time, you will notice:

1. a 'common.db' file is created
2. one of both executions advances freely; the other advances to the point "About to insert on ID: 0" and then gets locked until the first one is completed.