def _get_aws_credentials():
    """
    Returns the values stored in the AWS credential environment variables.
    Returns the value stored in the AWS_ACCESS_KEY_ID environment variable and
    the value stored in the AWS_SECRET_ACCESS_KEY environment variable.

    Returns
    -------
    out : tuple [string]
        The first string of the tuple is the value of the AWS_ACCESS_KEY_ID
        environment variable. The second string of the tuple is the value of the
        AWS_SECRET_ACCESS_KEY environment variable.

    Examples
    --------
    >>> turicreate.aws.get_credentials()
    ('RBZH792CTQPP7T435BGQ', '7x2hMqplWsLpU/qQCN6xAPKcmWo46TlPJXYTvKcv')
    """

    if (not 'AWS_ACCESS_KEY_ID' in _os.environ):
        raise KeyError('No access key found. Please set the environment variable AWS_ACCESS_KEY_ID.')
    if (not 'AWS_SECRET_ACCESS_KEY' in _os.environ):
        raise KeyError('No secret key found. Please set the environment variable AWS_SECRET_ACCESS_KEY.')
    return (_os.environ['AWS_ACCESS_KEY_ID'], _os.environ['AWS_SECRET_ACCESS_KEY'])