Meaning of += and -= in func _process(delta) in Godot

Question

In other languages like C and python

alpha += 3 would mean that at every iteration, value of alpha would increase by 3.
However, in Godot, += when it is within the function _process(delta) seems to maintain the value after every frame.
For example, if I set
var velocity +=50, the velocity value should keep increasing by 50 every frame. But, within the process function, the velocity seems to remain at the same value.
Is my reading correct? Am I missing something?
Can someone explain please?

Answer 1

It works the same. The only way it would not increase is if you have code like this.

func _process(delta):
    var velocity : float
    velocity += 50
    print(velocity)
    #this would print 50 every frame

This below will work

var velocity : float
func _process(delta):
    velocity += 50
    print(velocity)
    #this would add 50 every frame