Explain this codes line by line import os from my_app import app, db import unittest2 as unittest import tempfile

1. import os: This line imports the os module, which provides a way of using operating system dependent functionality like reading or writing to the file system.

2. from my_app import app, db: This line imports the app and db objects from the my_app module. These objects could be variables, functions, or classes defined in the my_app module.

3. import unittest2 as unittest: This line imports the unittest2 module and gives it an alias unittest. unittest2 is a unit testing framework for Python, providing a rich set of tools to construct and run tests.

4. import tempfile: This line imports the tempfile module, which provides functions for creating temporary files and directories.

Overall, these lines of code import the necessary modules and objects needed for unit testing a Flask application. The os and tempfile modules may be used to create temporary files or directories for testing purposes, while the app and db objects may be used to test application functionality. unittest2 is a popular testing framework that can be used to write and run unit tests for Python applications.