```__main__```is the name of the scopein which top-level code executes.

A module’s__name__isset equal to```__main__``` when readfrom standardinput, a script,orfrom an interactive prompt.

A module can discover whetherornot itis runningin the main scope by checking its own```__name__```, which allows a common idiomfor conditionally executing codein a module when itis runas a scriptorwith```python-m``` butnot when itis imported:

>>>if__name__=="__main__":

... main()

For a package, the same effect can be achieved by including a __main__.py module, the contents of which will be executed when the moduleis runwith-m

For example we are developing script whichis designed to be usedas module, we should do:

>>>def add(a, b):

...return a+b

>>> add(10,20)# we can test it by calling the function save it as calculate.py

>>>if__name__=="__main__":

... add(3,5)

>>>import calculate

>>> calculate.add(3,5)

1. Every Python module has it’s```__name__``` definedandif thisis```__main__```, it implies that the moduleis being run standalone by the userand we can do corresponding appropriate actions.

2. If youimport this scriptas a modulein another script, the__name__isset to the name of the script/module.

3. Python files can actas either reusable modules,oras standalone programs.

4.if```__name__== “main”:```is used to execute some code onlyif thefile was run directly,andnot imported.

The use of a Virtual Environmentis to test python codein encapsulated environmentsand to also avoid filling the base Python installationwith libraries we might usefor only one project.