On 12/07/20 8:13 AM, Peter J. Holzer wrote:
On 2020-07-11 09:54:33 +1200, dn via Python-list wrote:
Questions:
Is the idea of limiting the number of parameters passed across an interface
a real concern or somewhat an affectation?
Is three, five, seven, ... a valid limit (or warning-signal)?
Do you have a personal or corporate style or 'standard' to limit parameter
lists to seven parameters, or some other number?
Given that Python enables labeled arguments ("keyword arguments"), does the
concern really only apply to 'us' in terms of numbers of "positional
arguments"?
Keyword arguments greatly ameliorate the problems I have with long
parameter lists. While I think that calling a function with 7 positional
parameters is pretty much unreadable, with 7 named parameters (or maybe
2 positional and 5 named parameters) it doesn't bother me much. The
definition of the function might have even more parameters, as long as
most of them are optional and have sensible defaults (subprocess.Popen
with 20 parameters (if I counted correctly) is pushing it, though).
Do you think, then, that the maxima should be applied to the number of
arguments that will appear in the 'expected usage' of the routine? (cf
the def's parameter-list) After all, calling Popen would rarely require
all-20 arguments be stated, given the acceptability of the defaults and
the irrelevance of many 'special cases'.
Alternately/additionally, do you feel that the power and readability of
Python's keyword-arguments + default-values, requires a modification of
the advice to only limit the number of positional-arguments?
Another discussion-point (which may be difficult because 'the answer'
may vary according to implementation-requirements): rather than one
do-it-all 'Swiss Army Knife' of a routine with dozens of parameters,
might it be better-practice to code a number of methods/functions to
take care of the special-cases, with a single 'core function' to
carry-out the basic operations-required? (in a class environment:
sub-classes maybe)
Why not simply create and pass a collection (to suit the 'standards
committee') and be done. What's the big deal, don't have time to waste,
bureaucracy (!)...
What about the similar Q+D solution using a class?
That's what I often do. The main reason is that often a lot of those
parameters are repetitive. So instead of passing the same 7 parameters
to every function, I create a "Context" or "Job" class with those 7
fields which I then pass to each function. So it not just looks tidier,
it also reduces the risk of inconsistencies.
+1
Good thinking: promotes (indeed, dictates) consistency of interface!
--
Regards =dn
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