Language design

[Chris Angelico]

On Fri, Sep 13, 2013 at 4:13 AM, Markus Rother <python at markusrother.de> wrote:
> On 12.09.2013 01:27, Chris Angelico wrote:
>> On Thu, Sep 12, 2013 at 6:41 AM, Markus Rother <python at markusrother.de> wrote:
>>>     3. The default return value of methods is None instead of self.
>>>     If it was self, it would be possible to chain method calls (which
>>>     is called a cascade in smalltalk).
>>
>> That's a policy decision: a method (or function) will *EITHER* return
>> a value, *OR* mutate its primary argument (in the case of a method,
>> that's self).
>
> You are stating: "All getters must be free of side effects".
> That is not the case.  Furthermore, the demand for getters with hidden
> side effects is the reasoning behind properties.

This isn't a language feature here, just a stdlib policy. It's more
akin to Ruby's habit of adorning the mutating methods with an
exclamation mark - it's a way of stopping you from accidentally doing
what you didn't mean to do. There's a sharp distinction between
list.sort(), which mutates in place and returns None, and sorted(),
which doesn't touch its argument and returns a new list.

ChrisA