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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def s3_download(url, dst):
 # type: (str, str) -> None """Download a file from S3. Args: url (str):
 the s3 url of the file. dst (str):
 the destination where the file will be saved. """

    url = parse.urlparse(url)

    if url.scheme != 's3':
        raise ValueError("Expecting 's3' scheme, got: %s in %s" % (url.scheme, url))

    bucket, key = url.netloc, url.path.lstrip('/')

    region = os.environ.get('AWS_REGION', os.environ.get(_params.REGION_NAME_ENV))
    s3 = boto3.resource('s3', region_name=region)

    s3.Bucket(bucket).download_file(key, dst)