Why we use _ in python?

Answer 1

https://hackernoon.com/understanding-the-underscore-of-JUMP_LINK__&&__python__&&__JUMP_LINK-309d1a029edc

Answer 2

you cannot define a variable with space.
x y=5 #its wrong
but
x_y=5 #its right.

it's also use for if you want to define a variable with a name which is already built in function in python.
e.g

sum=4 #wrong because sum is built in function in python.
_sum=4 #right

it's also use in oop to tell the another programmer that this variable or function is private don't touch it.
_y=10 or def _h(): #private remember it's just convention to tell the another programmer but actual it is not a private.