prompter: Tell me the difference between object oriented and functional programming ?

assistant: In object oriented programming, you define objects with "fields" that store data, and "methods" that manipulate those fields. An object oriented program is usually formulated imperatively, defining step by step instructions to complete the calculation.

In functional programming, you write the output mathematically, as a function of the inputs. A functional program is usually formulated in terms of "pure" functions which do not have "side effects" like writing to variables.

prompter: Is that what's meant with idempotency?

assistant: Not exactly. Idempotence is a property of some operations or functions that means they have the same result no matter how many times you execute them12. For example, taking the absolute value of a number is idempotent because abs(abs(x)) = abs(x) for any x.

Object oriented and functional programming are different paradigms that describe how you write your code and structure your logic. They are not directly related to idempotence, although some functions in both paradigms may be idempotent or not depending on their definition and implementation.

assistant: A function is idempotent when its output fed back as input returns the same result. Here's a Python example:
```python
def absolute_value(x):
    """
    # Let's try a negative input [Test 1]
    >>> absolute_value(-1)
    1
    # Feed output as input [Test 2]
    >>> absolute_value(1)
    1
    # In one line of code [Test 2 wrapping Test 1]
    >>> absolute_value(absolute_value(-1))
    1
    """
    return x if x > 0 else -1 * x
```

prompter: How do object-oriented programming and functional programming compare to idempotency?

assistant: In object-oriented programming, idempotency is not a fundamental concept. While an object method may have a predictable output given a specific set of inputs, feeding its output as input may or may not produce the same result. It depends on whether the object's state has changed in between calls.

In functional programming, idempotency is a fundamental concept. Pure functions always produce the same output given the same input, no matter how many times they are called. They do not have side effects, so there is no hidden state that could affect the output.

So, in short, functional programming's focus on pure functions and lack of side effects make it easier to achieve idempotency, while object-oriented programming's reliance on stateful objects makes it more difficult.

assistant: In Object Oriented Programming, OOP for short, you make programs by using objects and calling their methods:

`form.submit()`

It is a great fit for GUI programming for example, and generally a approach closer to the physical world where you can push buttons to call an elevator, light up or print something.
Objects have an internal state and expose a public interface. It is very convenient to make sure that some internal invariants are always respected and to hide some complexity from users.
But it is easy for state mutations to generate unintended side effects.

Functional programming separate more cleanly data from logic applied to it, which prevent unintended side effects and can often compose more easily:

`reports = data.filter(is_valid).map(to_report).reduce(to_csv)`

It's a great fit for pipelines where components and combinators can be mixed together but it's generally less easy to optimize and less familiar for most programmers.

prompter: Yeah but isn't that just OOP with extra steps? 

In your example
```python 
data.filter(is_valid)
```
Still return a List (i.e. an "object") on which you do the rest of the operations. So what's the difference?