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    ```Python hl_lines="8-9"
    {!> ../../../docs_src/dependencies/tutorial005.py!}
    ```

It declares an optional query parameter `q` as a `str`, and then it just returns it.

This is quite simple (not very useful), but will help us focus on how the sub-dependencies work.

## Second dependency, "dependable" and "dependant"

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**Concurrency** and **parallelism** both relate to "different things happening more or less at the same time".

But the details between *concurrency* and *parallelism* are quite different.

To see the difference, imagine the following story about burgers:

### Concurrent Burgers

But if you need to change some of the defaults, support more than one predefined database, work with an async framework (like FastAPI), etc, you will need to add quite some complex extra code to override those defaults.

Nevertheless, it's possible to do it, and here you'll see exactly what code you have to add to be able to use Peewee with FastAPI.

!!! note "Technical Details"

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