How to use rosdep to install pyusb with pip with options(--pre)?

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Hello All,

I am trying to set pyusb as a runtime dependency, so I can use rosdep to install it. Here is the link to the install instructions. Link I tried adding python-usb as a dependency with libusb-1.0, but that did not work. It gave an error saying the "core" module could not be found.

I originally installed pyusb using the pip command from the previous link. So, looking up how to edit the rosdep rules, I thought I would add my own to install it using pip. I tried doing adding this to the python.yaml

pyusb:    
   ubuntu:
     pip:
        pyusb --pre

But upon doing that, it gave this as an error when I ran rosdep install:

ValueError: ('Expected version spec in', 'pyusb --pre', 'at', ' --pre')

I even tried adding the full command(which I believe I should be able to do based of this link.)

But that also gave an error. So how do I install pyusb with pip using rosdep and including the --pre option?

Thanks.