[Python-ideas] random.choice on non-sequence
Chris Barker - NOAA Federal
chris.barker at noaa.gov
Wed Apr 13 11:31:15 EDT 2016
> There's an upper limit on how dense a CPython dict or set can become
> (the load factor doesn't exceed 2/3), but no lower limit. For
> example, it's easy to end up with a dict holding a single entry hiding
> among millions of empty slots (dicts are never resized on key
> deletion, only on key insertion).
Easy, yes. Common? I wonder. If it were common then wouldn't there be
good reason to resize the hash table when that occurred? Aside from
being able to select random items, of course...
>> BTW, isn't it impossible to randomly select from an infinite iterable anyway?
> Of course, but it is possible to do uniform random selection, in one
> pass using constant space and in linear time, from an iterable whose
> length isn't known in advance (simple case of "reservoir sampling").
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