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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 get_aws_secrets_from_env():
 # type: () -> Set[str] """Extract AWS secrets from environment variables."""

    keys = set()
    for env_var in (
        'AWS_SECRET_ACCESS_KEY', 'AWS_SECURITY_TOKEN', 'AWS_SESSION_TOKEN',
    ):
        if env_var in os.environ:
            keys.add(os.environ[env_var])
    return keys