id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
33465	Introduce empty __slots__ protocol for SafeString & SafeData	Keryn Knight	Keryn Knight	"This is a case-by-case proposal ultimately referencing #12826

Because `SafeString` is used ''a lot'' and is otherwise supposed to be treatable as a untainted `str` we should be able to (AFAIK) update it + it's inheritance chain to use `__slots__ = ()` whilst still allowing custom subclasses of either to add additional attributes. By defining `__slots__` as empty on `SafeString` (**and** `SafeData`) we'd avoid creation of a `__dict__` on the instance, which mirrors the `str()` behaviour.

According to pympler, currently in Python `3.10` using the following back of the napkins strings:
{{{
In [4]: s = ""test""  # this might be interned, as a short string?

In [5]: s2 = ""test"" * 100

In [6]: s3 = SafeString(""test"")

In [7]: s4 = SafeString(""test"" * 100)
}}}
we get:
{{{
In [8]: asizeof(s)  # str
Out[8]: 56

In [9]: asizeof(s2)  # str
Out[9]: 456

In [10]: asizeof(s3)  # SafeString
Out[10]: 208

In [11]: asizeof(s4)  # SafeString
Out[11]: 608
}}}
But if we swap out the implementation to be slots'd, it looks more like:
{{{
In [8]: asizeof(s)  # str
Out[8]: 56

In [9]: asizeof(s2)  # str
Out[9]: 456

In [10]: asizeof(s3)  # SafeString
Out[10]: 104

In [11]: asizeof(s4)  # SafeString
Out[11]: 504
}}}

So we're ""saving"" `104 bytes` per `SafeString` created, by the look of it. I presume it to be some fun implementation detail of something somewhere that it is allegedly accounting for more than `64` bytes, which is the `asizeof({})`

A quick and dirty check over the test suite suggests that for me locally, running `14951 tests in 512.912s` accounted for `949.0 MB` of SafeStrings, checked by just incrementing a global integer of bytes (using `SafeString.__new__` and `--parallel=1`) and piping that to `filesizeformat`, so y'know, ''room for error''.
After the patch, the same tests accounted for `779.4 MB` of `SafeString`, ""saving"" `170 MB` overall.

The only functionality this would preclude -- as far as I know -- is no longer being able to bind arbitrary values to an instance like so:
{{{
s = SafeString('test')
s.test = 1
}}}
which would raise `AttributeError` if `__slots__` were added, just like trying to assign attributes to `str()` directly does.

I don't believe this will have any marked performance change, as neither `SafeString` nor `SafeData` actually have any extra attributes, only methods.

I have a branch which implements this, and tests pass for me locally."	Cleanup/optimization	assigned	Utilities	dev	Normal				Unreviewed	0	0	0	0	0	0