What is the size and length of the "rope" (ie. how much will it weigh), what orientation (eg. vertical or horizontal), and is it only supported by the switch?
How much force should be required to trigger the switch? If it's a vertical rope hanging on the switch, how much force should it be able to stand without pulling away from the switch (eg. breaking things).
Is it OK if it just detaches when pulled, or must it be "self resetting" so it works every time the rope is pulled.
As Billybob says, it's a mechanical layout problem and deciding on a suitable switch type depend on a lot of parameters.
It could be as simple as a jack plug attached to the string/rope that pulls out a jack socket & allows a contact to close, or a magnetic reed switch with a magnet attached to the rope - but the type depends on the physical layout and minimum/maximum forces etc.