[Marazan]

I'm sorry, I clearly haven't explained myself well as otherwise you would not have wasted a huge amount of text tying yourself in knots based clearly on a mistaken apprehension of what I was saying.

For clarity I reproduce the original function you gave and then I present what the change I am suggesting is

  def cool_function(x):
    for i in range(x):
      print(i)

My change

  def cool_function(x, output_stream=sys.stdout):
    for i in range(x):
      print(i, file=output_stream)

Does it now become clear what I am suggesting? My new function can be used as a 1-for-1 replacement for the old function, no code of the system needs changed as the default value provided to the new variable ensures semantically identical operation without changing any further code. Yet it is now unit testable

But now we can write a unit test like

  def test_output():
    output = io.StringIO()  
    cool_function(1, output)   
    contents = output.getvalue()
    assert contents=="1\n"

So I've made the code unit testable, kept semantics completely identical and not had to worrty about any weird IO concerns that you have. No monkey patching, no weird file IO, no bizarelly re-implemnting list(range(x)).

[byby]

> I'm sorry, I clearly haven't explained myself well as otherwise you would not have wasted a huge amount of text tying yourself in knots based clearly on a mistaken apprehension of what I was saying.

No need to apologize. This is a discussion. No one did anything wrong.

>For clarity I reproduce the original function you gave and then I present what the change I am suggesting is

This is called dependency injection and it's a valid way of segregating IO away from pure logic. Although this pattern is popular among old school OOP programmers it's getting out of vogue due to the complexity of it all. You used a python trick here of default values, but typically dependency injection changes the function signature and ups the complexity of the code by a lot. Let me show you the full output of the code that chatgpt was implying:

   #unit testable code (without using dependency injection tricks)

   def cool_function(x: int) -> None:
       IO_function(logic_function(x))

   def logic_function(x: int) -> List[int]:  
       return [i for i in range(x)]

   def IO_function(x: Any) -> None:
       print(x)
       
   def test_output():
       assert logic_function(4) == [i for i in range(4)]

Chatgpt only gave you logic_function, because IO_function is sort of obvious.. it's just "print" (I only wrapped print in "IO_function" to keep things clear, typically you won't define that function). But basically the full complete code would be to recompose IO with logic. You now have two components one of which is testable.

As a side note you will see it's actually an improvement to the code. It's simpler, no dependency injection, no confusing function type signature and a much simpler test case. The other thing that must be noted is the modularity.

Making tests unit testable in this way allows for your logic to be portable. What if I want to repurpose cool_function to output it's logic to another function? In your example you don't have the components to do that, it's harder for your case as you'd have to create another component for injection.

In short not only did chatGPT produce A correct answer. But it produced the better answer compared with your dependency injection. That being said your dependency injection is valid BUT you were not correct in saying that chatGPT's answer was worse or incorrect.

[byby]

>You've written 3 functions instead off one.

3 functions is better. Think about it. Do people write all their stuff in one big function? No. Better to compose higher level functions with smaller ones rather then write one big monolith like you did. The more modular something is the better.

Also IO_function is there for illustration purposes. Technically it's just wrapping print with a name so you can understand the intent. In reality you just use the regular print here without a wrapper, so in actuality only two functions are defined.

>The job of ChatGPT was to make cool_function unit testable. You haven't done it.

It did. By giving it a return value. Just like you did by giving it a new input value.

>You still have cool_function using side effect generating code hitting the actual IO system.

Yeah but one component of cool_function is pure and you can unit test that. Cool function itself can never be tested because it generates no output, you test the unit components of cool function. That's the point of unit tests.

>Genuinely the worst unit test I have ever seen written, on a poor form per line basis, absolute bananas. If you don't understand why [i for i in range(4)] is bad in a unit test and [0,1,2,3] is correct then I need you to walk away from the computer.

Let's just talk about it like adults. Just tell me what exactly about it makes you think it's bad?

Most likely it's some pedantic stylistic philosophy you have? I'm thinking you only want to test literals? Perhaps you prefer [0,1,2,3]? Am I right on the money?

Logic potentially has errors so you don't put logic in your test code. Makes sense, but who cares. For trivial shit it's fine. While in this case the logic in the test is identical to the function, typically 'logic_function' represents something significantly more complex and the list comprehension so I could care less if I'm not following the strictest form of testing. The comprehension is just something akin to an alias shortcut I prefer to use over writing out a massive literal. For the toy example the test is pointless because the logic is identical but typically it's fine to use range as an alias to represent a sequence of numbers.

Someone who strictly follows these stylistic rules without seeing intent or having the ability to bend the rules is just an inflexible pedantic programmer. It's not good to boast about it either by telling other people to walk away from a computer. That's just rude.