len() on mutables vs. immutables
tjreedy at udel.edu
Thu Oct 18 20:29:28 CEST 2012
On 10/18/2012 1:23 PM, Demian Brecht wrote:
> When len() is called passing an immutable built-in type (such as a
> string), I'd assume that the overhead in doing so is simply a function
> call and there are no on-call calculations done. Is that correct?
> I'd also assume that mutable built-in types (such as a bytearray) would
> cache their size internally as a side effect of mutation operations. Is
Or the length could be the difference of two pointers -- address of the
first empty slot minus address of first item.
> that correct? If so, is it safe to assume that at least all built-in
> types observe this behavior,
str, bytes, bytearrays, arrays, sets, frozensets, dicts, dictviews, and
ranges should all return len in O(1) time. That includes the possibility
of a subtraction as indicated above.
Terry Jan Reedy
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