If property does not exist, use default value in python I have a problem with my script, i want to let the user creating or not the property, but when the property is not used, blender give me an error (its normal).
i have tried things like:

if "myprop" not in own:
    own["myprop"] = MyValue


And

defaultValue = MyValue
value = own("myprop", defaultValue)


But nothing work, i allways get an error.

Maybe the second one can work, but i dont know how to use it correctly.

I have another question, my player use the Character physics, and in the physics menu, we have the Jump Force.
I want to set the Jump Force in python, i know the function for doing this is: 

jump_speed


But i dont know how tu use this:

GameObjectSettings(bpy_struct)


Thank you.
Extract and edited from my Movement script:

import bge

def main():

    cont = bge.logic.getCurrentController()
    own = cont.owner

# Verifier si les propriété existent.
Verif_Prop(own)

def Verif_Prop(own):

    # Verifie si la propriété existe.
    if "VitesseMarche" not in own:
        # Non définie, utiliser la valeur par défaut.
        own["VitesseMarche"] = 0.2


Source (i own the script): http://blenderartists.org/forum/showthread.php?381505-FR-EN-Advanced-Moving-Script-for-the-BGE-V2-0