Why does this error arise?

edit

I want to relabell the vertices of a randomly generated graph in Sage. Let $v$ be the set of vertices ordered according to their appearance in the degree sequence. The labelling strategy is like this:

1. Initialize: $k=0$

2. While $v\neq \emptyset$ do:

3. Pick the first element $u$ of $v$, $u\to k$, $k=k+1$

4. For $i$ in neighbors of $u$: $i\to k$, $k=k+1$. Remove $u$ and its neighbors from $v$.

In order to achieve that I wrote the following code but it gives me the folowing error: ValueError: list.remove(x): x not in list, which I do not know how to fix. I know that the problem is in the last part because the rest of the code works. In my understanding, all the elements of $s$ are also elements of $v$. So I do not know why the error is coming up.

     def t(n,m):
        G=graphs.RandomGNM(n,m)
        G.show()

        #***********forming the list b of tuples (vertex, deg(vertex))
        a=[]                                                         
        for i in G.vertices():
            a.append((i,G.degree(i)))          
        b=sorted(a, key=lambda x: x[1],reverse=True)

        #************** degree sequence  d of the graph G
        d=[]                                                                     
        for i in xrange(0,len(b)):                                               
            d.append(b[i][1])                                                    
        print("degree sequence",d)                                               

        #*************** sorting vertices in a list v according to the order they appear 
                        #in the degree sequence
        v=[]                                                                   
        for i in xrange(0,len(b)):                                               
            v.append(b[i][0])                                                    
        print("vertices       ",v)                                            

        #**************** relabelling vertices
        v_1=v[:]                                          
        v_2=list([0 for i in xrange(0,len(v))])  #~list which will hold the new labels 
        k=1
        while v<>[]:
            s=[]                                                              
            v_2[v_1.index(v[0])]=k   #relabeling the vertex with the highest degree in v
            s.append(v_1.index(v[0]))      
            k=k+1  
            for j in G.neighbors(v_1.index(v[0])): #~relabeling its neighbors
                v_2[v_1.index(j)]=k
                s.append(j)                
                k=k+1
            for f in s:   #removing from v the relabeled vertices
                v.remove(f)
        print(v_2)

UPDATE: The new code:

    def ver(d):#the function returns the list v of vertices  of the
           #Graph(d) in the order they appear in the degree sequence
    G=Graph(d)
    if G.vertices()<>[]:
        G.show()

    #*****forming the list b of tuples (vertex,deg(vertex))
    a=[]                                                         
    for i in G.vertices():
        a.append((i,G.degree(i)))          
    b=sorted(a, key=lambda x: x[1],reverse=True)

    #*****degree sequence  d of the graph G
    d=[]                                                                     
    for i in xrange(0,len(b)):                                               
        d.append(b[i][1])                                                                                                  

    #*****sorting vertices in a list v according to
    #**** the order they appear in the degree sequence
    v=[]                                                                   
    for i in xrange(0,len(b)):                                               
        v.append(b[i][0])                                                    
    print("vertices       ",v)                                            
    return(v) 


G=graphs.RandomGNM(10,14)
v=ver(G.to_dictionary())
v_1=v[:]
v_2=[0 for i in xrange(0,len(v))]
k=0
while v<>[]:
    v_2[v_1.index(v[0])]=k
    k=k+1
    for i in G.neighbors(v[0]):
        v_2[v_1.index(i)]=k
        k=k+1
    G.delete_vertices(G.neighbors(v[0]))
    G.delete_vertex(v[0])
    v=ver(G.to_dictionary())
d=dict(zip(v_1,v_2))
G.relabel(d)
G.show()

It works but G.show() does not produce any output.