human
Solve the following python programming problem given the following code:
def _get_ordering(son) : 
    'Helper function to extract formatted ordering from dict.
    ' 
    def fmt(field, direction) : 
        return '{0}{1}'.format ({ 
            (- 1) : '-', 
            1 : '+', 
} [direction], field) 
if ('$orderby' in son) : 
        return ', '.join ((fmt (f, son) for (f, d) in son ['$orderby'].items ())) 

    
    

    Fix the buggy line: return ', '.join ((fmt (f, son) for (f, d) in son ['$orderby'].items ()))
assistant
#Here is Python code to fix the buggy line: return ', '.

return ', '.join ((fmt (f, d) for (f, d) in son ['$orderby'].items ()))