```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

Underneath, the `open("./somefile.txt")` creates an object that is called a "Context Manager".

When the `with` block finishes, it makes sure to close the file, even if there were exceptions.

### <a href="https://www.django-rest-framework.org/" class="external-link" target="_blank">Django REST Framework</a> { #django-rest-framework }

Django REST framework was created to be a flexible toolkit for building Web APIs using Django underneath, to improve its API capabilities.

It is used by many companies including Mozilla, Red Hat and Eventbrite.

If you are using a Python version below 3.10, here's a tip from my very **subjective** point of view:

* 🚨 Avoid using `Optional[SomeType]`
* Instead ✨ **use `Union[SomeType, None]`** ✨.

Both are equivalent and underneath they are the same, but I would recommend `Union` instead of `Optional` because the word "**optional**" would seem to imply that the value is optional, and it actually means "it can be `None`", even if it's not optional and is still required.

    So, it's important to put this **near the end** of the `Dockerfile`, to optimize the container image build times.

6. Set the **command** to use `fastapi run`, which uses Uvicorn underneath.

    `CMD` takes a list of strings, each of these strings is what you would type in the command line separated by spaces.

## Very Technical Details { #very-technical-details }

/// warning

You can probably skip this.

These are very technical details of how **FastAPI** works underneath.

If you have quite some technical knowledge (coroutines, threads, blocking, etc.) and are curious about how FastAPI handles `async def` vs normal `def`, go ahead.

///

                    /* This is a key point. This is where we set the "tree" of this file which
                     * is like changing the rug out from underneath our feet.
                     */

would go, and broke off a bit of the edge with each hand.

  `And now which is which?' she said to herself, and nibbled a
little of the right-hand bit to try the effect:  the next moment
she felt a violent blow underneath her chin:  it had struck her
foot!

  She was a good deal frightened by this very sudden change, but
she felt that there was no time to be lost, as she was shrinking