You will see examples of this in the next chapters, about relational and NoSQL databases, security, etc.

## **FastAPI** compatibility

The simplicity of the dependency injection system makes **FastAPI** compatible with:

* all the relational databases
* NoSQL databases
* external packages
* external APIs
* authentication and authorization systems
* API usage monitoring systems

		var fw fileWriter
		switch maker := v.maker.(type) {
		case makeReg:
			fw = &regFileWriter{w, maker.size}
			wantStr = maker.wantStr
		case makeSparse:
			if !validateSparseEntries(maker.sph, maker.size) {
				t.Fatalf("invalid sparse map: %v", maker.sph)
			}
			spd := invertSparseEntries(maker.sph, maker.size)
			fw = &regFileWriter{w, maker.makeReg.size}
			fw = &sparseFileWriter{fw, spd, 0}

> Modern versions of Python have support for **"asynchronous code"** using something called **"coroutines"**, with **`async` and `await`** syntax.

That should make more sense now. ✨

All that is what powers FastAPI (through Starlette) and what makes it have such an impressive performance.

## Very Technical Details

/// warning

You can probably skip this.

	data.Delimiter = s3EncodeName(delimiter, encodingType)
	data.MaxKeys = maxKeys

	data.NextKeyMarker = s3EncodeName(resp.NextMarker, encodingType)
	data.NextVersionIDMarker = resp.NextVersionIDMarker
	data.VersionIDMarker = versionIDMarker
	data.IsTruncated = resp.IsTruncated

	prefixes := make([]CommonPrefix, 0, len(resp.Prefixes))
	for _, prefix := range resp.Prefixes {

		var fr fileReader
		switch maker := v.maker.(type) {
		case makeReg:
			r := testNonEmptyReader{strings.NewReader(maker.str)}
			fr = &regFileReader{r, maker.size}
		case makeSparse:
			if !validateSparseEntries(maker.spd, maker.size) {
				t.Fatalf("invalid sparse map: %v", maker.spd)
			}
			sph := invertSparseEntries(maker.spd, maker.size)
			r := testNonEmptyReader{strings.NewReader(maker.makeReg.str)}

	ListObjects(ctx context.Context, bucket, prefix, marker, delimiter string, maxKeys int) (result ListObjectsInfo, err error)
	ListObjectsV2(ctx context.Context, bucket, prefix, continuationToken, delimiter string, maxKeys int, fetchOwner bool, startAfter string) (result ListObjectsV2Info, err error)
	ListObjectVersions(ctx context.Context, bucket, prefix, marker, versionMarker, delimiter string, maxKeys int) (result ListObjectVersionsInfo, err error)

In GitHub, the template will guide you to write the right question so that you can more easily get a good answer, or even solve the problem yourself even before asking. And in GitHub I can make sure I always answer everything, even if it takes some time. I can't personally do that with the chat systems. 😅

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	Objects   uint64
	Versions  uint64 // Versions that are not delete markers.
	ObjSizes  sizeHistogram
	Compacted bool
}

//msgp:tuple dataUsageEntryV6
type dataUsageEntryV6 struct {
	Children dataUsageHashMap
	// These fields do no include any children.
	Size      int64
	Objects   uint64
	Versions  uint64 // Versions that are not delete markers.
	ObjSizes  sizeHistogram
	Compacted bool
}

So:

```Python
q: Union[str, None] = Query(default=None)
```

...makes the parameter optional, with a default value of `None`, the same as:

```Python
q: Union[str, None] = None
```

And in Python 3.10 and above:

```Python
q: str | None = Query(default=None)
```

...makes the parameter optional, with a default value of `None`, the same as:

```Python