How do you create an indexable empty list in python?

Is there a way to neatly create large (i.e. indexable) empty lists in python?

This is what I am doing at the moment:

firstgen=G.neighbors(node1)
secgen=[]
thirdgen=[[],[],[],[],[],[],[],[],[],[],[]]  #11 brackets because len(secgen)=11

for i in firstgen:
    secgen.append(G.neighbors(i))   

for i in range(len(secgen)):
    for j in secgen[i]:
        thirdg开发者_如何学Pythonen[i].append(G.neighbors(j))

What I am doing is finding the neighbors of the neighbors of the neighbors of an original node in a network and so my third generation list of neighbors should have the structure [ [[...],[...],[...]] , [[...],[...],[...]] , [[...],[...],[...]] ] but I am new to python and have not been able to find how to make this work without manually putting in the length of thirdgen.

Sorry for the confusing explanation. I am doing this in order to find triads in the network i.e. if any of the third gen nodes are the same as the initial node then I have found a triad.

Thanks!

EDIT: I just realised that I can simply put thirdgen.append([]) in the first loop. Still curious about other methods though.

You don't need to create the empty lists. You can use list comprehensions to build your nested lists:

firstgen = G.neighbors(node1)
secndgen = [G.neighbors(node) for node in firstgen]
thirdgen = [[G.neighbors(node) for node in group] for group in secndgen]

• firstgen: [node, ...]
• secndgen: [[node, ...], ...]
• thirdgen: [[[node, ...], ...], ...]

Perhaps:

thirdgen = [list() for x in range(len(secgen))]
thirdgen = [list() for x in range(11)]

Or I might be misunderstanding the actual question.

You could use list generator as follows: [[] for x in range(11)].