</p>

<p>
On machines where <code>SP</code> and <code>PC</code> are
traditionally aliases for a physical, numbered register,
in the Go assembler the names <code>SP</code> and <code>PC</code>
are still treated specially;
for instance, references to <code>SP</code> require a symbol,
much like <code>FP</code>.
To access the actual hardware register use the true <code>R</code> name.
For example, on the ARM architecture the hardware

	hm := hmac.New(sha1.New, []byte(secretAccessKey))
	hm.Write([]byte(stringToSign))

	// Calculate signature.
	signature := base64.StdEncoding.EncodeToString(hm.Sum(nil))

	query := req.URL.Query()
	// Handle specially for Google Cloud Storage.
	query.Set("AWSAccessKeyId", accessKeyID)
	// Fill in Expires for presigned query.
	query.Set("Expires", strconv.FormatInt(epochExpires, 10))

	// Encode query and save.

	// http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectDELETE.html
	objInfo, err := deleteObject(ctx, bucket, object, opts)
	if err != nil {
		if _, ok := err.(BucketNotFound); ok {
			// When bucket doesn't exist specially handle it.
			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
			return
		}
		if isErrObjectNotFound(err) || isErrVersionNotFound(err) {
			// Send an event when the object is not found

    ([CVE-2020-26270](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26270))
*   Fixes a security vulnerability caused by accessing heap data outside of
    bounds when loading a specially crafted `SavedModel`
    ([CVE-2020-26271](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26271))
*   Solves an OOM issue on TPUs when XLA contexts use fused average updates

* kubernetes will try to acquire the iptables lock every 100 msec during 5 seconds instead of every second. This specially useful for environments using kube-proxy in iptables mode with a high churn rate of services. ([#85771](https://github.com/kubernetes/kubernetes/pull/85771), [@aojea](https://github.com/aojea))

// https://www.iana.org/domains/root/db/dubai.html
dubai

// dunlop : The Goodyear Tire & Rubber Company
// https://www.iana.org/domains/root/db/dunlop.html
dunlop

// dupont : DuPont Specialty Products USA, LLC
// https://www.iana.org/domains/root/db/dupont.html
dupont

// durban : ZA Central Registry NPC trading as ZA Central Registry
// https://www.iana.org/domains/root/db/durban.html
durban

In an expression switch, the cases contain expressions that are compared
against the value of the switch expression.
In a type switch, the cases contain types that are compared against the
type of a specially annotated switch expression.
The switch expression is evaluated exactly once in a switch statement.
</p>

<h4 id="Expression_switches">Expression switches</h4>

<p>
In an expression switch,

    * PR [#235](https://github.com/tiangolo/fastapi/pull/235).

* Fix OpenAPI documentation of Starlette URL convertors. Specially useful when using `path` convertors, to take a whole path as a parameter, like `/some/url/{p:path}`. PR [#234](https://github.com/tiangolo/fastapi/pull/234) by [@euri10](https://github.com/euri10).