Question 1

import math vs from math import sqrt

Accepted Answer

'import math' binds the name 'math' in your namespace. You access everything through that name as math.sqrt, math.pi, and so on. 'from math import sqrt' pulls sqrt directly into your namespace, so you call it as sqrt(x) without a prefix. The module is loaded the same way in both cases - the difference is only which names land in your local namespace. Prefer 'import math' in larger files so readers always know where a function came from. Use 'from ... import' when you need a name constantly and the source is obvious from context.

Question 2

What if __name__ == '__main__': does

Accepted Answer

When Python runs a file directly, it sets __name__ to '__main__'. When the same file is imported as a module, __name__ is set to the module's name instead. The guard lets you put test code, a CLI entry point, or setup logic at the bottom of a file without that code firing every time someone imports the module. Every script that might also be imported should have this guard - without it, top-level code runs on import, which is almost never what you want.

Question 3

What __init__.py does in a package

Accepted Answer

Before Python 3.3, a directory needed __init__.py to be treated as a package at all. When you write 'import mypackage', Python executes mypackage/__init__.py. You can leave it empty (just a marker file) or use it to set up the public API - importing submodules, defining __all__, or running initialization code. A common pattern is to re-export the most-used names so callers can write 'from mypackage import MyClass' instead of 'from mypackage.core import MyClass'.

Question 4

__name__ value when imported

Accepted Answer

Python sets __name__ to the module's fully qualified name when a file is imported. For a top-level file named utils.py, that name is 'utils'. For a submodule like mypackage/utils.py imported as 'from mypackage import utils', __name__ would be 'mypackage.utils'. The value '__main__' is reserved for the script that Python runs directly. Knowing this lets you write code that behaves differently depending on whether it is being run or imported - which is exactly what the if __name__ == '__main__' guard relies on.

Question 5

import alias with 'as'

Accepted Answer

'import math as m' binds the module to the name 'm' and does not create a binding for 'math'. So m.floor(3.7) works fine and returns 3 (floor rounds down). But 'math.floor(3.7)' raises NameError because 'math' is not in scope. Aliases are common in data science (import numpy as np, import pandas as pd) precisely because they shorten repetitive qualified names. The tradeoff is that someone reading the code must know the alias conventions. If you alias a module, every access in that file must go through the alias - you cannot mix math.x and m.x.