And it's possible that for your use case, the solution is in one of them.

///

## Read the Tutorial first { #read-the-tutorial-first }

The next sections assume you already read the main [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

	}

	// ErrKeyExists is an error returned by the KMS when trying to
	// create a key that already exists.
	ErrKeyExists = Error{
		Code:    http.StatusConflict,
		APICode: "kms:KeyAlreadyExists",
		Err:     "key with given key ID already exits",
	}

	// ErrKeyNotFound is an error returned by the KMS when trying to
	// use a key that does not exist.
	ErrKeyNotFound = Error{

				if strings.Contains(err.Error(), "The requested address is not valid in its context") {
					// Ignore if IP is unbindable.
					continue nextTest
				}
				if strings.Contains(err.Error(), "bind: address already in use") {
					continue nextTest
				}
				t.Fatalf("Test %d: error: expected = <nil>, got = %v", i+1, err)
			}
		}

		for _, serverAddr := range listener.Addrs() {

You could still use most of the features in **FastAPI** with the knowledge from the main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank}.

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=409, detail="Item already exists")
    fake_db[item.id] = item

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=409, detail="Item already exists")
    fake_db[item.id] = item

# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/fastapi/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment

	}

	req, err := http.NewRequest(http.MethodPost, target.args.Endpoint.String(), bytes.NewReader(data))
	if err != nil {
		return err
	}

	// Verify if the authToken already contains
	// <Key> <Token> like format, if this is
	// already present we can blindly use the
	// authToken as is instead of adding 'Bearer'
	tokens := strings.Fields(target.args.AuthToken)
	switch len(tokens) {
	case 2:

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=409, detail="Item already exists")
    fake_db[item.id] = item

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=409, detail="Item already exists")
    fake_db[item.id] = item