[docs] frozenset.copy() does not create a copy

INADA Naoki songofacandy at gmail.com
Tue May 8 04:28:12 EDT 2018

On Tue, May 8, 2018 at 5:20 PM Mihail Temelkov <mtemelkov at gmail.com> wrote:

> Tried it in Python 2.7 and found that it just creates an alias to the
original set.

In Python, copy() or similar methods may return itself for immutable types.
It's widely used optimization.

>>> t=(1,2)
>>> t1=(1,2)
>>> t2=t1[:]
>>> t1 is t2

And it is implementation (CPython) specific optimization; other
may return new instance.
You shouldn't rely on undocumented behavior.

INADA Naoki  <songofacandy at gmail.com>

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