Rant (was Re: x*x if x>10

[DaveM]

Re: Rant (was Re: x*x if x>10

On Sun, 27 Jul 2008 19:46:32 +0200, "Diez B. Roggisch" <deets@nospam.w eb.de>
wrote:

>As a rule of thumb, don't return objects you didn't create inside a
>function from scratch.

I wish I'd had that advice when I started learning python. It would have
saved me no end of grief.

DaveM

[Terry Reedy]

Re: Rant (was Re: x*x if x&gt;10



DaveM wrote:

On Sun, 27 Jul 2008 19:46:32 +0200, "Diez B. Roggisch" <deets@nospam.w eb.de>
wrote:

>As a rule of thumb, don't return objects you didn't create inside a
>function from scratch.

Unless its job is specifically to get/fetch an object (reference
thereto) from someplace the caller cannot or should not access. But
then it should probably not mutate the object before returning the
reference.

>
I wish I'd had that advice when I started learning python. It would have
saved me no end of grief.

I wish I had seen this 'rule' before too.

[Diez B. Roggisch]

Re: Rant (was Re: x*x if x&gt;10

Terry Reedy schrieb:

>
>
DaveM wrote:

>On Sun, 27 Jul 2008 19:46:32 +0200, "Diez B. Roggisch"
><deets@nospam. web.de>
>wrote:

>>As a rule of thumb, don't return objects you didn't create inside a
>>function from scratch.

>
Unless its job is specifically to get/fetch an object (reference
thereto) from someplace the caller cannot or should not access. But
then it should probably not mutate the object before returning the
reference.

I maybe should paraphrase "don't return objects you passed as arguments
from a function". Of course there are exceptions to this rule - but
these are few, the canonical being chained function calls like this:


class Whatever(object ):

def do_something(se lf, arguments):
....
return self



Diez

[greg]

Re: Rant (was Re: x*x if x&gt;10

Diez B. Roggisch wrote:

I maybe should paraphrase "don't return objects you passed as arguments
from a function".

The important thing is that a function shouldn't modify
any object unless it's the express purpose of the function
to do so.

You could call this the "look but don't touch" rule.

--
Greg