def download_fileobj(
    self, Bucket, Key, Fileobj, ExtraArgs=None, Callback=None, Config=None
):
    """Download an object from S3 to a file-like object.

    The file-like object must be in binary mode.

    This is a managed transfer which will perform a multipart download in
    multiple threads if necessary.

    Usage::

        import boto3
        s3 = boto3.client('s3')

        with open('filename', 'wb') as data:
            s3.download_fileobj('amzn-s3-demo-bucket', 'mykey', data)

    :type Bucket: str
    :param Bucket: The name of the bucket to download from.

    :type Key: str
    :param Key: The name of the key to download from.

    :type Fileobj: a file-like object
    :param Fileobj: A file-like object to download into. At a minimum, it must
        implement the `write` method and must accept bytes.

    :type ExtraArgs: dict
    :param ExtraArgs: Extra arguments that may be passed to the
        client operation. For allowed download arguments see
        :py:attr:`boto3.s3.transfer.S3Transfer.ALLOWED_DOWNLOAD_ARGS`.

    :type Callback: function
    :param Callback: A method which takes a number of bytes transferred to
        be periodically called during the download.

    :type Config: boto3.s3.transfer.TransferConfig
    :param Config: The transfer configuration to be used when performing the
        download.
    """
    if not hasattr(Fileobj, 'write'):
        raise ValueError('Fileobj must implement write')

    subscribers = None
    if Callback is not None:
        subscribers = [ProgressCallbackInvoker(Callback)]

    config = Config
    if config is None:
        config = TransferConfig()

    new_config = python_copy.copy(config)
    disable_threading_if_append_mode(new_config, Fileobj)

    with create_transfer_manager(self, new_config) as manager:
        future = manager.download(
            bucket=Bucket,
            key=Key,
            fileobj=Fileobj,
            extra_args=ExtraArgs,
            subscribers=subscribers,
        )
        return future.result()
Download an object from S3 to a file-like object.

    The file-like object must be in binary mode.

    This is a managed transfer which will perform a multipart download in
    multiple threads if necessary.

    Usage::

        import boto3
        s3 = boto3.client('s3')

        with open('filename', 'wb') as data:
            s3.download_fileobj('amzn-s3-demo-bucket', 'mykey', data)

    :type Bucket: str
    :param Bucket: The name of the bucket to download from.

    :type Key: str
    :param Key: The name of the key to download from.

    :type Fileobj: a file-like object
    :param Fileobj: A file-like object to download into. At a minimum, it must
        implement the `write` method and must accept bytes.

    :type ExtraArgs: dict
    :param ExtraArgs: Extra arguments that may be passed to the
        client operation. For allowed download arguments see
        :py:attr:`boto3.s3.transfer.S3Transfer.ALLOWED_DOWNLOAD_ARGS`.

    :type Callback: function
    :param Callback: A method which takes a number of bytes transferred to
        be periodically called during the download.

    :type Config: boto3.s3.transfer.TransferConfig
    :param Config: The transfer configuration to be used when performing the
        download.
    
boto3/s3/inject.py