Returns all symbols defined in an ast node. 
    
    if ctx_types is given, then restrict the symbols to ones with that context.
    
    :param node: ast node
    :param ctx_types: type or tuple of types that may be found assigned to the `ctx` attribute of 
                      an ast Name node.

def get_symbols(node, ctx_types=(ast.Load, ast.Store)):
    '''
    Returns all symbols defined in an ast node. 
    
    if ctx_types is given, then restrict the symbols to ones with that context.
    
    :param node: ast node
    :param ctx_types: type or tuple of types that may be found assigned to the `ctx` attribute of 
                      an ast Name node.
        
    '''
    gen = SymbolVisitor(ctx_types)
    return gen.visit(node)