Question

Lets assume I have defined function:

def threeArgs(x,y,z):
  return ... # Returns True or False

I also have a list of elements:

a = [elem1, elem2, ..., elemN]

I would like to construct another list b containing first and last element form list a and those elements Xn in between for which threeArgs(Xn-1,Xn, Xn+1) returns true.

How to do it in elegant pythonic way?

Answer 1

Use slicing to create three shifted lists, then zip them together:

[a[0]] + [y for x, y, z in zip(a, a[1:], a[2:]) if threeArgs(x, y, z)] + [a[-1]]