Python/Q#: Module not found error, with .qs file in the same directory

Question

Lately I started working with Q# and python as host language. I was working on a project and everything seemed fine. Suddenly I get the error "module not found" and I seem to get it in all my previous projects too.

So I have a directory: C:\Users\Username\Q#projects In this folder I have 2 files: HostProtocol.py, which is the main file, and BB84.qs, which is the file from which I want to import.

The HostProtocol.py file looks like this:

import qsharp

from Quantum.BB84 import Run_BB84Protocol
Run_BB84Protocol.simulate()

The BB84.qs file looks like this:

namespace Quantum.BB84 {
    open Microsoft.Quantum.Arrays;
    open Microsoft.Quantum.Measurement;
    open Microsoft.Quantum.Canon;
    open Microsoft.Quantum.Intrinsic;
    open Microsoft.Quantum.Diagnostics;
    open Microsoft.Quantum.Convert;
    open Microsoft.Quantum.Math;

function Run_BB84Protocol() Unit{... the code from the function...}
}

When I try to run HostProtocol.py I get the following error message:

Exception has occurred: ModuleNotFoundError No module named 'Quantum' File "C:\Users\Username\Q#projects\HostProtocol.py", line 3, in from Quantum.BB84 import Run_BB84Protocol

And this is for all my previous projects too. It's very frustrating and I have no clue what could have caused it because it worked fine previously. Any help is definitely welcome!

Answer 1

If you have any Q# compilation errors in your Q# source file, your Q# operations and functions will not be available. Check your Python output for errors. When I run the sample code you provided, it reports a syntax error in the Q# code (there's a missing colon before the return type Unit ):

 fail: Microsoft.Quantum.IQSharp.Workspace[0]
       QS3211: Invalid return type annotation. The argument tuple needs to be followed
       by a colon and the return type of the callable.