On 01Mar2017 21:25, Serhiy Storchaka <[email protected]> wrote:
On 28.02.17 23:17, Victor Stinner wrote:
My question is: would it make sense to implement this feature in
Python directly? If yes, what should be the syntax? Use "/" marker?
Use the @positional() decorator?
I'm strongly +1 for supporting positional-only parameters. The main
benefit to me is that this allows to declare functions that takes
arbitrary keyword arguments like Formatter.format() or
MutableMapping.update(). Now we can't use even the "self" parameter
and need to use a trick with parsing *args manually. This harms clearness and
performance.
I was a mild +0.1 on this until I saw this argument; now I am +1 (unless
there's some horrible unforseen performance penalty).
I've been writing quite a few functions lately where it is reasonable for a
caller to want to pass arbitrary keyword arguments, but where I also want some
additional parameters for control purposes. The most recent example was
database related: functions accepting arbitrary keyword arguments indicating
column values.
As a specific example, what I _want_ to write includes this method:
def update(self, where, **column_values):
Now, because "where" happens to be an SQL keyword it is unlikely that there
will be a column of that name, _if_ the database is human designed by an SQL
person. I have other examples where picking a "safe" name is harder. I can even
describe scenarios where "where" is plausible: supposing the the database is
generated from some input data, perhaps supplied by a CSV file (worse, a CSV
file that is an export of a human written spreadsheet with a "Where" column
header). That isn't really even made up: I've got functions whose purpose is
to import such spreadsheet exports, making namedtuple subclasses automatically
from the column headers.
In many of these situations I've had recently positional-only arguments would
have been very helpful. I even had to bugfix a function recently where a
positional argument was being trouced by a keyword argument by a caller.
Cheers,
Cameron Simpson <[email protected]>
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