def get_left_indexes(var, expected_dims):
    """Returns a tuple for the extra leftmost dimension sizes.
    
    For example, if an algorithm expects a 3 dimensional variable, but the 
    variable includes an additional left dimension for Time, and 
    this Time dimension has 3 values, then this function will return (3,).
    
    Args:
    
        var (array): An array object that contains the :attr:`ndim` 
            and :attr:`shape` attributes.
            
        expected_dims (:obj:`int`): The expected number of dimensions (usually
            for a computational algorithm).
            
    Returns:
    
        :obj:`tuple`: The shape for the extra leftmost dimensions.
    
    """
    extra_dim_num = var.ndim - expected_dims
    
    if (extra_dim_num == 0):
        return []
    
    return var.shape[0:extra_dim_num]