if data_str is not None:
        for line in data_str.splitlines():
            lines.append(f"data: {line}")

    if id is not None:
        lines.append(f"id: {id}")

    if retry is not None:
        lines.append(f"retry: {retry}")

    lines.append("")
    lines.append("")
    return "\n".join(lines).encode("utf-8")


# Keep-alive comment, per the SSE spec recommendation

{* ../../docs_src/query_param_models/tutorial001_an_py310.py hl[9:13,17] *}

**FastAPI** will **extract** the data for **each field** from the **query parameters** in the request and give you the Pydantic model you defined.

## Check the Docs { #check-the-docs }

You can see the query parameters in the docs UI at `/docs`:

<div class="screenshot">
<img src="/img/tutorial/query-param-models/image01.png">

So, what we will do next is add the code to document how that *external API* should look like to receive the callback from *your API*.

That documentation will show up in the Swagger UI at `/docs` in your API, and it will let external developers know how to build the *external API*.

This example doesn't implement the callback itself (that could be just a line of code), only the documentation part.

/// tip

     *            {@link org.apache.maven.building.Problem.Severity#ERROR}.
     * @param source A hint about the source of the problem like a file path, may be {@code null}.
     * @param lineNumber The one-based index of the line containing the problem or {@code -1} if unknown.
     * @param columnNumber The one-based index of the column containing the problem or {@code -1} if unknown.

# o applicationBehaviorMap: (NotRequired - Default map:{})
# o outputPackageAdjustmentMap: (NotRequired - Default map:{})
# o dbfluteSystemFinalTimeZone: (NotRequired - Default null)
#
# *The line that starts with '#' means comment-out.
#
map:{
    # /- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    # o database: (Required)
    #  This is the target database, only considered when generating

    /**
     * Indicates whether the model should track the line/column number of the model source from which it was parsed.
     *
     * @return {@code true} if location tracking is enabled, {@code false} otherwise.
     */
    boolean isLocationTracking();

    /**
     * Enables/disables the tracking of line/column numbers for the model source being parsed. By default, input

	}
	return data
}

// ScanLines is a split function for a [Scanner] that returns each line of
// text, stripped of any trailing end-of-line marker. The returned line may
// be empty. The end-of-line marker is one optional carriage return followed
// by one mandatory newline. In regular expression notation, it is `\r?\n`.
// The last non-empty line of input will be returned even if it has no
// newline.

		}
	}
	in.Push(NewTokenizer(name, fd, fd))
}

// #line processing.
func (in *Input) line() {
	// Only need to handle Plan 9 format: #line 337 "filename"
	tok := in.Stack.Next()
	if tok != scanner.Int {
		in.expectText("expected line number after #line")
	}
	line, err := strconv.Atoi(in.Stack.Text())
	if err != nil {
		in.Error("error parsing #line (cannot happen):", err)
	}
	tok = in.Stack.Next()

    }

    /**
     * Creates a string with all location details for the specified model problem. If the project identifier is
     * provided, the generated location will omit the model id and source information and only give line/column
     * information for problems originating directly from this POM.
     *
     * @param problem The problem whose location should be formatted, must not be {@code null}.

When we don't need to declare more validations or metadata, we can make the `q` query parameter required just by not declaring a default value, like:

```Python
q: str
```

instead of:

```Python
q: str | None = None
```

But we are now declaring it with `Query`, for example like:

```Python
q: Annotated[str | None, Query(min_length=3)] = None
```