This seems sensible to me. I remember Guido vetoing allowing
random.choice() to accept a set, and for the same reason - it encourages
inefficient code.
Rob Cliffe
On 16/06/2021 15:50, Oliver Margetts wrote:
Hi all, I came across the following performance issue with the sum
function while summing lists: https://bugs.python.org/issue18305
<https://bugs.python.org/issue18305> It's been discussed previously in
this list and other issues.
The rationale in that ticket makes the case that performance won't be
fixed because sum() should not be treated as a generic way to
concatenate sequences (and there is documentation saying this).
Having non-linear complexity is not a suitable way to discourage this
behaviour though. Non-linearity is hard to detect in testing and
development, so is more likely to lead to performance bugs in
libraries and production, than to discourage use from the outset.
Moreover, it is confusing to end users to have a feature while
discouraging its use through a somewhat passive-aggressive runtime.
New users, and experienced users who do not pour through the
documentation will use sum because it supports this API, and one would
assume that's intentional.
On the other hand, the behaviour for strings is a far superior
user-experience. When attempting to use sum() on strings, users are
presented with a TypeError and a handy tip (use "".join(seq) instead).
It is clear to users that they are attempting an anti-pattern and how
to correct it.
So I propose moving (eventually) to the same system with lists as for
strings. Or else removing the performance trip-hazard from the sum
function with lists.
Best regards,
Oliver
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