def download_file(url, dest=None, chunk_size=1024, replace="ask",
                  label="Downloading {dest_basename} ({size:.2f}MB)",
                  expected_extension=None):
    """Download a file from a given URL and display progress.

    :param dest: If the destination exists and is a directory, the filename
        will be guessed from the Content-Disposition header. If the destination
        is an existing file, the user will either be prompted to overwrite, or
        the file will be replaced (depending on the value of **replace**). If
        the destination does not exist, it will be used as the filename.
    :param int chunk_size: bytes read in at a time.
    :param replace: If `False`, an existing destination file will not be
        overwritten.
    :param label: a string which is formatted and displayed as the progress bar
        label. Variables provided include *dest_basename*, *dest*, and *size*.
    :param expected_extension: if set, the filename will be sanitized to ensure
        it has the given extension. The extension should not start with a dot
        (`.`).
    """
    dest = Path(dest or url.split("/")[-1])
    response = get(url, stream=True)
    if (dest.exists()
            and dest.is_dir()
            and "Content-Disposition" in response.headers):
        content_disposition = rfc6266.parse_requests_response(response)
        if expected_extension is not None:
            filename = content_disposition.filename_sanitized(
                expected_extension)
        filename = secure_filename(filename)
        dest = dest / filename
    if dest.exists() and not dest.is_dir():
        if (replace is False
                or replace == "ask"
                and not click.confirm("Replace {}?".format(dest))):
            return str(dest)
    size = int(response.headers.get("content-length", 0))
    label = label.format(dest=dest, dest_basename=dest.name,
                         size=size/1024.0/1024)
    with click.open_file(str(dest), "wb") as f:
        content_iter = response.iter_content(chunk_size=chunk_size)
        with click.progressbar(content_iter, length=size/1024,
                               label=label) as bar:
            for chunk in bar:
                if chunk:
                    f.write(chunk)
                    f.flush()
    return str(dest)
async def _post_initial(
        self,
        body: "_models.CalculateExchangeRequest",
        **kwargs: Any
    ) -> Optional["_models.CalculateExchangeOperationResultResponse"]:
        cls = kwargs.pop('cls', None)  # type: ClsType[Optional["_models.CalculateExchangeOperationResultResponse"]]
        error_map = {
            401: ClientAuthenticationError, 404: ResourceNotFoundError, 409: ResourceExistsError
        }
        error_map.update(kwargs.pop('error_map', {}))
        api_version = "2020-10-01-preview"
        content_type = kwargs.pop("content_type", "application/json")
        accept = "application/json"

        # Construct URL
        url = self._post_initial.metadata['url']  # type: ignore

        # Construct parameters
        query_parameters = {}  # type: Dict[str, Any]
        query_parameters['api-version'] = self._serialize.query("api_version", api_version, 'str')

        # Construct headers
        header_parameters = {}  # type: Dict[str, Any]
        header_parameters['Content-Type'] = self._serialize.header("content_type", content_type, 'str')
        header_parameters['Accept'] = self._serialize.header("accept", accept, 'str')

        body_content_kwargs = {}  # type: Dict[str, Any]
        body_content = self._serialize.body(body, 'CalculateExchangeRequest')
        body_content_kwargs['content'] = body_content
        request = self._client.post(url, query_parameters, header_parameters, **body_content_kwargs)
        pipeline_response = await self._client._pipeline.run(request, stream=False, **kwargs)
        response = pipeline_response.http_response

        if response.status_code not in [200, 202]:
            map_error(status_code=response.status_code, response=response, error_map=error_map)
            error = self._deserialize.failsafe_deserialize(_models.Error, response)
            raise HttpResponseError(response=response, model=error, error_format=ARMErrorFormat)

        response_headers = {}
        deserialized = None
        if response.status_code == 200:
            deserialized = self._deserialize('CalculateExchangeOperationResultResponse', pipeline_response)

        if response.status_code == 202:
            response_headers['Azure-AsyncOperation']=self._deserialize('str', response.headers.get('Azure-AsyncOperation'))
            response_headers['Location']=self._deserialize('str', response.headers.get('Location'))
            response_headers['Retry-After']=self._deserialize('int', response.headers.get('Retry-After'))

        if cls:
            return cls(pipeline_response, deserialized, response_headers)

        return deserialized