How can I avoid sp.TOption type when using sp.unpack()?

Question

Within my smartpy contract, I want to convert from one type into another using sp.pack() and sp.unpack.

Below is an example of the method I am trying to use, converting a string to bytes.

        myString = sp.local("myString", "dummyString")
        packedString = sp.pack(myString.value)
        myBytes = sp.unpack(packedString, t = sp.TBytes)

The problem is the type of the output I get is

sp.TOption(sp.TBytes)

when what I wanted was just

sp.TBytes

What else should I do to make sure the type isn't sp.TOption?

Answer 1

sp.unpack gives you an option (because Michelson gives an option when you call UNPACK) that you need to open.

You can do it like this

        myBytes = sp.unpack(packedString, t = sp.TBytes).open_some()

if you're sure that packedString is indeed a packed sp.TBytes.

If you're not 100% sure, you can add an optional error message to open_some().