[Python-ideas] __before__ and __after__ attributes for functions

[Suresh V.]

On Thursday 30 January 2014 02:14 PM, Ronald Oussoren wrote:
>
> On 24 Jan 2014, at 08:54, Suresh V. <suresh_vv at yahoo.com> wrote:
>
>> On Friday 24 January 2014 10:39 AM, Ethan Furman wrote:
>>> On 01/23/2014 08:09 PM, Suresh V. wrote:
>>>>
>>>> Also it would mean that the client code imports from this package.
>>>> I would like client code to remain exactly as it is (continue to
>>>> import from its original package) but the behavior is enhanced
>>>> once this package is imported on startup.
>>>
>>> /Something/ has to adjust the pre and post conditions -- if not the
>>> client code, then what?
>>
>> pre and post conditions are just one possible use of this.
>>
>> Going back to my smtplib.SMTP.sendmail example.
>> No changes in bulk of client code.
>> Single patch module imported in main.
>
> Why is this a good thing? You seem to propose adding a mechanism that makes it easily possible to modify the behaviour of existing functions, which makes it harder to reason about code.

It is a "good thing" because it adheres to the "Open/Closed principle" 
better than monkey patching does. Meaning open to extension and closed 
to modification.

>
> While this is also possible without language changes with the current monkey patching mechanisms its at least clear that your doing something naughty when writing the patching code :-)

This if for those non-naughty times :-)