On 7/29/2011 8:50 PM, Steven D'Aprano wrote:
Guido has a rule of thumb: "No constant arguments". Or another way to put
it: if a function takes an argument which is nearly always a constant
(usually, but not always, a flag) then it is usually better off as two
functions.
I do not really understand his 'rule'*. The stdlib has lots of functions
with boolean flags and params which default to None and are seldom
over-ridden.
* Which is to say, it feels more like his gut feeling applied on a
case-by-case basis than an actual rule that anyone could apply in any
objective manner.
Especially if the implementation looks like this:
def get_thing(argument, flag):
if flag:
return one_thing(argument)
else:
return another_thing(argument)
If the rule is limited to this situation, where no code is shared, it
seems pretty sensible.
Argument flags which do nothing but change the behaviour of the function
from Mode 1 to Mode 2 are an attractive nuisance: they seem like a good
idea, but aren't. Consider it a strong guideline rather than a law, but
it's one I would think very long and hard about before violating.
But having said that, I'm currently writing a library where nearly all the
functions violate the No Constant Argument rule. (The API isn't yet stable,
so I may still change my mind.) Make of that what you will.
See * above ;-).
Terry Jan Reedy
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