global and nonlocal scope instance problems in Python

The reason is this: I want to launch GUI interface to let customers choose some activities, and serialize the user's choices to local, and at the same time, I want to continue to remember the user's choices in memory, so that I can continue to use them later.

import pickle import tkinter app = tkinter.Tk() def selenium_handler_yingxiao(): all_activity_name = ["Xi'an guest economy-Smart enterprise-Community Shop dispatch list", "2020 Xi'an community store-Single wide to financial marketing", "Xi'an community store-Collection of arrears with account age of 2 months"] try: activity_record = pickle.load(open('4to5.pckl', 'rb')) except FileNotFoundError: # If the file does not exist, create and reset print("File does not exist, new and reset") activity_record = [] if len(activity_record) == 0: # If the read content is empty, open the GUI for setting op_mark = [tkinter.IntVar() for _ in all_activity_name] for variable, text in zip(op_mark, all_activity_name): tkinter.Checkbutton(text=text, variable=variable).pack() def change(): global activity_record activity_record = [text for variable, text in zip(op_mark, all_activity_name) if variable.get()] pickle.dump(activity_record, open('4to5.pckl', 'wb')) print("The activity we want to call is 1:", id(activity_record), activity_record) app.quit() tkinter.Button(app, text="confirm", command=change).pack() app.mainloop() print("The activities we want to call are 2:", id(activity_record), activity_record) selenium_handler_yingxiao() print("The activities we want to call are:", id(activity_record), activity_record)

I expect the output of both activities to be the same, but the actual output is as follows:

Why does this happen?

This is because of the global activity in the function change()_ Record statement changes the variable activity_record is declared as a global variable, but as long as it is still in the function selenium_ handler_ In the scope of yingxiao(), activity_record is still selenium_ handler_ The local variable of the yingxiao() function. In selenium_ handler_ Beyond the scope of the yingxiao() function, we can still get the user's selection normally.

So, if we want to use the function selenium_ handler_ At the end of yingxiao(), you can get the activity selected by the user normally. What should you do?

The first way: we can_ handler_ The variable activity is declared in the yingxiao() function_ Record is the global activity_record), so global activity is declared in two places_ record，selenium_ handler_ The variables in yingxiao () become real global variables.

import pickle import tkinter app = tkinter.Tk() def selenium_handler_yingxiao(): global activity_record all_activity_name = ["Xi'an guest economy-Smart enterprise-Community Shop dispatch list", "2020 Xi'an community store-Single wide to financial marketing", "Xi'an community store-Collection of arrears with account age of 2 months"] try: activity_record = pickle.load(open('4to5.pckl', 'rb')) except FileNotFoundError: # If the file does not exist, create and reset print("File does not exist, new and reset") activity_record = [] if len(activity_record) == 0: # If the read content is empty, open the GUI for setting op_mark = [tkinter.IntVar() for _ in all_activity_name] for variable, text in zip(op_mark, all_activity_name): tkinter.Checkbutton(text=text, variable=variable).pack() def change(): global activity_record activity_record = [text for variable, text in zip(op_mark, all_activity_name) if variable.get()] pickle.dump(activity_record, open('4to5.pckl', 'wb')) print("The activity we want to call is 1:", id(activity_record), activity_record) app.quit() tkinter.Button(app, text="confirm", command=change).pack() app.mainloop() print("The activities we want to call are 2:", id(activity_record), activity_record) selenium_handler_yingxiao() print("The activities we want to call are:", id(activity_record), activity_record)

Second method: we can declare non local activity in function change()_ Record, in this way, the variable activity declared by nonlocal_ Record is neither a local variable nor a global variable, but an external nested function selenium_ handler_ The variables in yingxiao (), that is, after you declare them like this, you can think of selenium_ handler_ Activity of yingxiao()_ Activity of record and inner nested function change()_ Record is the same variable.

import pickle import tkinter app = tkinter.Tk() def selenium_handler_yingxiao(): all_activity_name = ["Xi'an guest economy-Smart enterprise-Community Shop dispatch list", "2020 Xi'an community store-Single wide to financial marketing", "Xi'an community store-Collection of arrears with account age of 2 months"] try: activity_record = pickle.load(open('4to5.pckl', 'rb')) except FileNotFoundError: # If the file does not exist, create and reset print("File does not exist, new and reset") activity_record = [] if len(activity_record) == 0: # If the read content is empty, open the GUI for setting op_mark = [tkinter.IntVar() for _ in all_activity_name] for variable, text in zip(op_mark, all_activity_name): tkinter.Checkbutton(text=text, variable=variable).pack() def change(): nonlocal activity_record activity_record = [text for variable, text in zip(op_mark, all_activity_name) if variable.get()] pickle.dump(activity_record, open('4to5.pckl', 'wb')) print("The activity we want to call is 1:", id(activity_record), activity_record) app.quit() tkinter.Button(app, text="confirm", command=change).pack() app.mainloop() print("The activities we want to call are 2:", id(activity_record), activity_record) selenium_handler_yingxiao() # print("the activity we want to call is:", id(activity_record), activity_record)

Of course, at this time, if no special return operation is carried out, in selenium_ handler_ Outside of the yingxiao() function, the activity cannot be obtained_ Of the record variable.

4 June 2020, 22:06 | Views: 7160