human
Solve the following python programming problem given the following code:
@ not_implemented_for ('multigraph') 
def astar_path(G, source, target, heuristic = None, weight = 'weight') : 
    'Return a list of nodes in a shortest path between source and target
    using the A* ("A-star") algorithm.

    There may be more than one shortest path.  This returns only one.

    Parameters
    ----------
    G : NetworkX graph

    source : node
       Starting node for path

    target : node
       Ending node for path

    heuristic : function
       A function to evaluate the estimate of the distance
       from the a node to the target.  The function takes
       two nodes arguments and must return a number.

    weight: string, optional (default=\'weight\')
       Edge data key corresponding to the edge weight.

    Raises
    ------
    NetworkXNoPath
        If no path exists between source and target.

    Examples
    --------
    >>> G=nx.path_graph(5)
    >>> print(nx.astar_path(G,0,4))
    [0, 1, 2, 3, 4]
    >>> G=nx.grid_graph(dim=[3,3])  # nodes are two-tuples (x,y)
    >>> def dist(a, b):
    ...    (x1, y1) = a
    ...    (x2, y2) = b
    ...    return ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
    >>> print(nx.astar_path(G,(0,0),(2,2),dist))
    [(0, 0), (0, 1), (1, 1), (1, 2), (2, 2)]

    See Also
    --------
    shortest_path, dijkstra_path

    ' 
    if ((source not in G) or (target not in G)) : 
        msg = 'Either source {} or target {} is not in G' 
        raise nx.NodeNotFound (msg.format (source, target)) 
if (heuristic is None) : 
        def heuristic(u, v) : 
            return 0 
push = heappush 
    pop = heappop 
    c = count () 
    queue = [(0, next (c), source, 0, None)] 
    enqueued = { 
        
} 
    explored = { 
        
} 
    while queue : 
        (_, __, curnode, dist, parent) = pop (queue) 
        if (curnode == target) : 
            path = [curnode] 
            node = parent 
            while (node is not None) : 
                path.append (node) 
                node = explored [node] 
path.reverse () 
            return path...

    
    

    Fix the buggy line: if (curnode in pop) :
assistant
#Here is Python code to fix the buggy line: if (curnode in pop) :
.

if (curnode in explored) :