Question

What is wrong with the following?:

lss = reduce(list.extend, [[1],[2]], [])

causes:

Traceback (most recent call last):
  File "<pyshell#230>", line 1, in <module>
    lss = reduce(list.extend, [[1],[2]], [])
TypeError: descriptor 'extend' requires a 'list' object but received a 'NoneType'

I’m not sure where the NoneType is coming from.

Answer 1

Try this instead:

lss = reduce(lambda acc, ele : acc + ele, [[1],[2]], [])

lss
> [1, 2]

The problem is that extend() returns None (that’s where the NoneType is coming from), and that won’t work with what you want to do – the function passed to reduce() must return a value: the accumulated result so far.