On Jun 29, 2018, at 5:32 PM, Abe Dillon <[email protected]> wrote:
>
> Sure, but in Hettinger's own words "whenever you have a constructor war,
> everyone should get their wish". People that want a counting constructor have
> that,
> people that want the ability to initialize values don't have that.
Sorry Abe, but you're twisting my words and pushing very hard for a proposal
that doesn't make sense and isn't necessary.
* Counts initialized to zero: This isn't necessary. The whole point of
counters is that counts default to zero without pre-initialization.
* Counts initialized to one: This is already done by the regular constructor.
Use "Counter(keys)" if the keys are known to be unique and "Counter(set(keys)"
to ignore duplicates.
>>> Counter('abc')
Counter({'a': 1, 'b': 1, 'c': 1})
>>> Counter(set('abbacac'))
Counter({'a': 1, 'b': 1, 'c': 1})
* Counts initialized to some other value: That would be an unusual thing to do
but would be easy with the current API.
>>> Counter(dict.fromkeys('abc', 21))
Counter({'a': 21, 'b': 21, 'c': 21})
* Note, the reason that fromkeys() is disabled is that it has nonsensical or
surprising interpretations:
>>> Counter.fromkeys('aaabbc', 2) # What should this do that
doesn't surprise at least some users?
* That reason is already shown in the source code.
@classmethod
def fromkeys(cls, iterable, v=None):
# There is no equivalent method for counters because setting v=1
# means that no element can have a count greater than one.
raise NotImplementedError(
'Counter.fromkeys() is undefined. Use Counter(iterable)
instead.')
> Obviously, Python breaks SOLID principals successfully all over the place for
> pragmatic reasons.
> I don't think this is one of those cases.
No amount of citing generic design principles will justify adding an API that
doesn't make sense.
Besides, any possible use cases already have reasonable solutions using the
existing API. That is likely why no one has ever requested this behavior
before.
Based on what I've read in this thread, I see nothing that would change the
long-standing decision not to have a fromkeys() method for collections.Counter.
The original reasoning still holds.
Raymond
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