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