set Fall and Jump speed character physics

I have an object with a character physics setting.
Every time I press the mouse button it should set the fall speed of the object to zero and stop it in midair.
I’m able to set the gravity, the only problem is how to set the object’s fall and and jump speed velocity at run time

My code’s like this at the moment

import GameLogic
from bge import logic

cont = GameLogic.getCurrentController()

own = cont.owner

controller = bge.constraints.getCharacter(own)

object = logic.getCurrentScene().objects

obj = object["player_collision_box.001"]    #the main object 

attack = cont.sensors["attack"]    #the mouse sensor 

if attack.positive:
    controller.gravity = 0

    own["Timer"] = 0.000 = 0.0    #doesn't work = 0.0

elif own["Timer"] > 0.4: #Timer property used to set how long gravity stops acting on the object
    controller.gravity = 9.8