## Import `Header` { #import-header }

First import `Header`:

{* ../../docs_src/header_params/tutorial001_an_py310.py hl[3] *}

## Declare `Header` parameters { #declare-header-parameters }

Then declare the header parameters using the same structure as with `Path`, `Query` and `Cookie`.

You can define the default value as well as all the extra validation or annotation parameters:

Interceptors can be chained. Suppose you have both a compressing interceptor and a checksumming interceptor: you'll need to decide whether data is compressed and then checksummed, or checksummed and then compressed. OkHttp uses lists to track interceptors, and interceptors are called in order.

![Interceptors Diagram](../assets/images/******@****.***)

### Application Interceptors

in any such claim at its own expense.

For example, a Contributor might include the Program in a commercial product
offering, Product X. That Contributor is then a Commercial Contributor. If
that Commercial Contributor then makes performance claims, or offers warranties
related to Product X, those performance claims and warranties are such Commercial

    }

    /**
     * Delays the crawler while waiting for new URLs to be available.
     * This method calibrates CPU load, checks crawler status, applies
     * interval control rules, and then calls the parent implementation.
     */
    @Override
    protected void delayForWaitingNewUrl() {
        ComponentUtil.getSystemHelper().calibrateCpuLoad();
        try {

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and then install it, for example:

```console
$ pip install python-multipart
```

///

## Import `Form` { #import-form }

Import `Form` from `fastapi`:

    curl -s -q https://dl.min.io/client/mc/release/linux-${TARGETARCH}/mc.sha256sum -o /go/bin/mc.sha256sum && \
    chmod +x /go/bin/mc

RUN if [ "$TARGETARCH" = "amd64" ]; then \
       curl -L -s -q https://github.com/moparisthebest/static-curl/releases/latest/download/curl-${TARGETARCH} -o /go/bin/curl; \
       chmod +x /go/bin/curl; \
    fi

      d="$${d#bazel-out/*/bin/}"

      if [[ $${d} == *local_config_* ]]; then
        continue
      fi

      if [[ $${d} == external* ]]; then
        extname="$${d#*external/}"
        extname="$${extname%%/*}"
        if [[ $${TF_SYSTEM_LIBS:-} == *$${extname}* ]]; then
          continue
        fi

        d="$${d#*external/farmhash_archive/src}"

      // Fail fast if there's no response queued up.
      return failFastResponse!!
    }

    val result = responseQueue.take()

    // If take() returned because we're shutting down, then enqueue another dead letter so that any
    // other threads waiting on take() will also return.
    if (result == DEAD_LETTER) responseQueue.add(DEAD_LETTER)

    return result
  }

   *     #hasNext()}
   */
  @ParametricNullness
  E peek();

  /**
   * {@inheritDoc}
   *
   * <p>The objects returned by consecutive calls to {@link #peek()} then {@link #next()} are
   * guaranteed to be equal to each other.
   */
  @CanIgnoreReturnValue
  @Override
  @ParametricNullness
  E next();

  /**
   * {@inheritDoc}
   *

		return nil, fmt.Errorf("'%s' does not have a valid range value", rangeString)
	}

	offsetBeginString := byteRangeString[:sepIndex]
	offsetBegin := int64(-1)
	// Convert offsetBeginString only if its not empty.
	if len(offsetBeginString) > 0 {
		if offsetBeginString[0] == '+' {
			return nil, fmt.Errorf("Byte position ('%s') must not have a sign", offsetBeginString)