Question about the usage of list about 2021-03-18-server-code-design HOT 3 CLOSED

Good question. The db variable is defined at the top of module outside of any function. This makes it a "global" variable. So, it is accessible within any function (with certain important exceptions). And, since it is a list, it can be appended and changed without needing to use the global command in the function (as long as you don't try to erase it using a line such as db=[]. That will cause the variable to revert to a local variable).

So, when the add_patient_to_db function is run, and it comes to line 21 where db is referenced. Since no new db variable has been created in this function, Python looks to the global workspace and finds db there, and modifies it as needed. A global variable should not be included in the parameter list of the function definition, nor should it be returned.

Then, that brings up your next question about how do you test a function when it modifies a global variable and then doesn't return it. I went over this specific test in class on Thursday. Please review the Panopto Recording from Thursday (found at https://pratt.capture.duke.edu/Panopto/Pages/Viewer.aspx?id=c4d86e48-8380-4f03-849d-acf60167251e) and look at the section starting at 12:03 of the recording. I give an example of how you can test a function that modifies a global variable.

The code for this testing example can be found in my ClassworkSpring2021 repository on the server_design branch in a file called test_health_db_server.py and is linked here:
https://github.com/dward2/ClassworkSpring2021/blob/eef72f529319c7c159e0179761903d4e2e3f836c/test_health_db_server.py#L1-L13

Let me know if you have any further questions or if my explanation isn't clear.

from 2021-03-18-server-code-design.

@minhuiyu0418 I'm tagging you to this issue to make sure that you were alerted to my reply. Please visit the issue and look at my previous comment.

from 2021-03-18-server-code-design.

@dward2 Thank you it's very clear!

from 2021-03-18-server-code-design.