On 10/18/2012 3:18 PM, Prasad, Ramit wrote:
Terry Reedy wrote:
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?
See below.
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.
Why does pointer arithmetic work for dicts?
It would only possibly be for lists, bytearrays, and, array module
arrays.They are all over-allocated and need pointer to beginning, and
either len or pointers to current end and allocated end. The current
authoritative answer is in the current code itself.
--
Terry Jan Reedy
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