Question

Sorry for the awkward title but I’ll explain better here;

In the function below;

def returnList():
  list = []
  for i in xrange(4):
    list.append(i)

  return list

It returns the list [0,1,2,3]. In another function;

def returnAllLists():
  totalList = []
  for i in xrange(4):
    totalList.append(returnList())

  return totalList

As expected it turns a result like

[[1,2,3,4],[1,2,3,4],[1,2,3,4],[1,2,3,4]]

. The tricky part is that I need the result

[1,2,3,4,1,2,3,4,1,2,3,4,1,2,3,4]

. I can of course easily assign the result of returnAllList to another list and go for two loops and insert the elements individually into another list however I think a more efficient way could be done since my method has an O(N^2) complexity just for assigning same values in a different way. Any suggestions?

Answer 1

Use extend() in place of append():

 totalList.extend(returnList())

Does exactly what you want.