Why is it a mistake to assign the result of list.append()?
New users will often write code like:
seq =  for i in range(10): seq = seq.append(i)
… And become confused when it crashes with
AttributeError: 'NoneType' object has no attribute 'append'.
They assume that
list.append returns a reference to the original list, but it actually returns None. The solution is to call
.append without assigning the result to anything.
seq =  for i in range(10): seq.append(i)