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[Python-Dev] configparser: should optionxform be idempotent?

Inada Naoki songofacandy at gmail.com
Thu Mar 7 05:06:31 EST 2019 
On Thu, Mar 7, 2019 at 6:57 PM Paul Moore <p.f.moore at gmail.com> wrote:
>
> I'm not keen on the term "idempotent" here - I wasn't at all clear
> what it was intended to convey. But from looking at the bug report, I
> see that it basically means "optionxform should be a function which,
> when applied more than one time to a value, returns the same result as
> if it had been applied once only".

You're right.  "idempotent" is technical (or mathematical) jargon.
When f(x) satisfies "f(x) == f(f(x)) for all x" restriction, f(x) is idempotent.


>
> I'd look at the question the other way round. If we *did* insist that
> optionxform has to be "idempotent", how would we recommend that the
> person who reported the bug achieved the result he's trying to get?
> lambda x: x if x.startswith("(") and x.endswith(")") else "(" + x +
> ")"? That seems a bit fiddly.

In this case, we recommend not using optionxform to wrap name with
"()" implicitly.  Use wrapped name explicitly instead.

e.g. cfg["section"]["(name)"] = "value"

It's very simple.

-- 
Inada Naoki  <songofacandy at gmail.com>
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