# Custom Response Classes - File, HTML, Redirect, Streaming, etc.

There are several custom response classes you can use to create an instance and return them directly from your *path operations*.

Read more about it in the [FastAPI docs for Custom Response - HTML, Stream, File, others](https://fastapi.tiangolo.com/advanced/custom-response/).

You can import them directly from `fastapi.responses`:

```python
from fastapi.responses import (
    FileResponse,

<p>
Some symbols, such as <code>R1</code> or <code>LR</code>,
are predefined and refer to registers.
The exact set depends on the architecture.
</p>

<p>
There are four predeclared symbols that refer to pseudo-registers.
These are not real registers, but rather virtual registers maintained by
the toolchain, such as a frame pointer.
The set of pseudo-registers is the same for all architectures:
</p>

<ul>

func (p *parallelReader) Done() {
	if p.stashBuffer != nil {
		globalBytePoolCap.Load().Put(p.stashBuffer)
		p.stashBuffer = nil
	}
}

// preferReaders can mark readers as preferred.
// These will be chosen before others.
func (p *parallelReader) preferReaders(prefer []bool) {
	if len(prefer) != len(p.orgReaders) {
		return
	}
	// Copy so we don't change our input.
	tmp := make([]io.ReaderAt, len(p.orgReaders))

The same would happen if you had something like a <abbr title='A union between multiple types means "any of these types".'>union</abbr> between different types where one or more of them are not valid Pydantic types, for example this would fail 💥:

{* ../../docs_src/response_model/tutorial003_04_py310.py hl[8] *}

<img src="/img/tutorial/security/image02.png">

/// note

It doesn't matter what you type in the form, it won't work yet. But we'll get there.

///

This is of course not the frontend for the final users, but it's a great automatic tool to document interactively all your API.

It can be used by the frontend team (that can also be yourself).

  reached or started.

  All of these operations will produce their own unique errors in the absence of
  a coordinated offline strategy. In addition, efforts to unite these failing
  behaviors behind a consistent user interface is much, much more difficult if
  the system can't tell whether it has access to the network required by these
  operations.

 *   <li>{@linkplain State#RUNNING RUNNING} -&gt;
 *   <li>{@linkplain State#STOPPING STOPPING} -&gt;
 *   <li>{@linkplain State#TERMINATED TERMINATED}
 * </ul>
 *
 * <p>There are deviations from this if there are failures or if {@link Service#stopAsync} is called
 * before the {@link Service} reaches the {@linkplain State#RUNNING RUNNING} state. The set of legal

The OAuth2 specification defines "scopes" as a list of strings separated by spaces.

The content of each of these strings can have any format, but should not contain spaces.

These scopes represent "permissions".

In OpenAPI (e.g. the API docs), you can define "security schemes".

When one of these security schemes uses OAuth2, you can also declare and use scopes.

Each "scope" is just a string (without spaces).

### Suggest solutions { #suggest-solutions }

* After being able to understand the question, you can give them a possible **answer**.

* In many cases, it's better to understand their **underlying problem or use case**, because there might be a better way to solve it than what they are trying to do.

In these cases, you would normally return an **HTTP status code** in the range of **400** (from 400 to 499).

This is similar to the 200 HTTP status codes (from 200 to 299). Those "200" status codes mean that somehow there was a "success" in the request.

The status codes in the 400 range mean that there was an error from the client.

Remember all those **"404 Not Found"** errors (and jokes)?

## Use `HTTPException` { #use-httpexception }