Meaning A.1 package exists;
A: A program module too, need to create a folder to manage these modules, there will be a package of concepts;
A.2 Python3 will automatically identify files in the project folder at this time does not need new __init__.py file, the program will automatically go to identify each folder (but regulatory requirements need to build each package __init__.py file), but Pthon2 not going to recognize these packages, that is, as long as the package had to have __init__ file;