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typing.Set (built-in set type) is aliased to collections.abc.Set (abstract set) #264

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layday opened this issue May 3, 2022 · 7 comments

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@layday
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layday commented May 3, 2022

  • cattrs version: 22.1.0
  • Python version: 3.8
  • Operating System: macOS

Description

GenConverter's unstruct_collection_overrides param expects a collections.abc.Set in Python 3.9+ and a typing.Set in Python 3.8 and below. typing.Set is a generic version of the set built-in; the typing module's equivalent of collections.abc.Set is AbstractSet. In 3.8 and below, collections.abc.Set is silently ignored and typing.Set incorrectly applies to all set types. I would expect collections.abc.Set to work on all (supported) Python versions, especially considering that paremetrised overrides are not supported (Set[...] has no effect).

What I Did

from collections.abc import Set

converter = GenConverter(unstruct_collection_overrides={Set: sorted})
converter.unstructure(frozenset(()))  # Not converted to a list on Python 3.8
@Tinche
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Tinche commented May 4, 2022

Ooph, let's see, it's a little confusing.

On 3.8 and below, collections.abc.Set doesn't support subscripting (collections.abc.Set[int] is an error) so I don't think it's worth supporting. I believe on those versions the recommendation is to use the typing alternatives.

I think supporting typing.AbstractSet does make sense on those versions. So a collection override for typing.AbstractSet would apply to MutableSet, builtin sets, and frozen sets.

Since typing.AbstractSet was deprecated in 3.9, I don't think it's important to support it on those versions - on 3.9+ we would expect the users to switch to the collections.abc variants.

When I say I don't consider something worth supporting, I'm doing some cost/benefit analysis of the maintenance burden of all these combinations, and as you see there are a lot of them.

So in your case, your snippet (on 3.8) would need to become:

from typing import AbstractSet

converter = GenConverter(unstruct_collection_overrides={AbstractSet: sorted})
converter.unstructure(frozenset(()))

That sound good?

@layday
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layday commented May 4, 2022

On 3.8 and below, collections.abc.Set doesn't support subscripting (collections.abc.Set[int] is an error)

But collection overrides themselves don't support subscripting, right? GenConverter(unstruct_collection_overrides={collections.abc.Set[int]: sorted}) won't do anything. Arguably, the converter should raise for unsupported overrides. Is there a reason not to support collections.abc.Set across all Python versions? Anyway, either typing.AbstractSet or collections.abc.Set would be fine :)

@Tinche
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Tinche commented May 4, 2022

Started working on this here: #266

The docs say this feature isn't supported on versions prior to 3.9 btw, and I remember why not - it's very gnarly to get right across all the versions :/

@Tinche
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Tinche commented May 5, 2022

I've merged this to main, can you verify the behavior is what you'd expect?

@layday
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layday commented May 5, 2022

That's done the trick, thanks :) And I'm sorry, I missed the notice about 3.9 somehow.

@Tinche
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Tinche commented May 5, 2022

Cool, ok if I close this?

@layday
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layday commented May 5, 2022

Yep, thanks.

@Tinche Tinche closed this as completed May 5, 2022
mergify bot pushed a commit to aws/jsii that referenced this issue Oct 3, 2022
…3 in /packages/@jsii/python-runtime (#3785)

Updates the requirements on [cattrs](https://github.com/python-attrs/cattrs) to permit the latest version.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/python-attrs/cattrs/blob/main/HISTORY.rst">cattrs's changelog</a>.</em></p>
<blockquote>
<h2>22.2.0 (2022-10-03)</h2>
<ul>
<li><em>Potentially breaking</em>: <code>cattrs.Converter</code> has been renamed to <code>cattrs.BaseConverter</code>, and <code>cattrs.GenConverter</code> to <code>cattrs.Converter</code>.
The <code>GenConverter</code> name is still available for backwards compatibility, but is deprecated.
If you were depending on functionality specific to the old <code>Converter</code>, change your import to <code>from cattrs import BaseConverter</code>.</li>
<li><code>NewTypes &lt;https://docs.python.org/3/library/typing.html#newtype&gt;</code>_ are now supported by the <code>cattrs.Converter</code>.
(<code>[#255](python-attrs/cattrs#255) &lt;https://github.com/python-attrs/cattrs/pull/255&gt;</code><em>, <code>[#94](python-attrs/cattrs#94) &lt;https://github.com/python-attrs/cattrs/issues/94&gt;</code></em>, <code>[#297](python-attrs/cattrs#297) &lt;https://github.com/python-attrs/cattrs/issues/297&gt;</code>_)</li>
<li><code>cattrs.Converter</code> and <code>cattrs.BaseConverter</code> can now copy themselves using the <code>copy</code> method.
(<code>[#284](python-attrs/cattrs#284) &lt;https://github.com/python-attrs/cattrs/pull/284&gt;</code>_)</li>
<li>Python 3.11 support.</li>
<li>cattrs now supports un/structuring <code>kw_only</code> fields on attrs classes into/from dictionaries.
(<code>[#247](python-attrs/cattrs#247) &lt;https://github.com/python-attrs/cattrs/pull/247&gt;</code>_)</li>
<li>PyPy support (and tests, using a minimal Hypothesis profile) restored.
(<code>[#253](python-attrs/cattrs#253) &lt;https://github.com/python-attrs/cattrs/issues/253&gt;</code>_)</li>
<li>Fix propagating the <code>detailed_validation</code> flag to mapping and counter structuring generators.</li>
<li>Fix <code>typing.Set</code> applying too broadly when used with the <code>GenConverter.unstruct_collection_overrides</code> parameter on Python versions below 3.9. Switch to <code>typing.AbstractSet</code> on those versions to restore the old behavior.
(<code>[#264](python-attrs/cattrs#264) &lt;https://github.com/python-attrs/cattrs/issues/264&gt;</code>_)</li>
<li>Uncap the required Python version, to avoid problems detailed in <a href="https://iscinumpy.dev/post/bound-version-constraints/#pinning-the-python-version-is-special">https://iscinumpy.dev/post/bound-version-constraints/#pinning-the-python-version-is-special</a>
(<code>[#275](python-attrs/cattrs#275) &lt;https://github.com/python-attrs/cattrs/issues/275&gt;</code>_)</li>
<li>Fix <code>Converter.register_structure_hook_factory</code> and <code>cattrs.gen.make_dict_unstructure_fn</code> type annotations.
(<code>[#281](python-attrs/cattrs#281) &lt;https://github.com/python-attrs/cattrs/issues/281&gt;</code>_)</li>
<li>Expose all error classes in the <code>cattr.errors</code> namespace. Note that it is deprecated, just use <code>cattrs.errors</code>.
(<code>[#252](python-attrs/cattrs#252) &lt;https://github.com/python-attrs/cattrs/issues/252&gt;</code>_)</li>
<li>Fix generating structuring functions for types with quotes in the name.
(<code>[#291](python-attrs/cattrs#291) &lt;https://github.com/python-attrs/cattrs/issues/291&gt;</code>_ <code>[#277](python-attrs/cattrs#277) &lt;https://github.com/python-attrs/cattrs/issues/277&gt;</code>_)</li>
<li>Fix usage of notes for the final version of <code>PEP 678 &lt;https://peps.python.org/pep-0678/&gt;</code><em>, supported since <code>exceptiongroup&gt;=1.0.0rc4</code>.
(<code>[#303](python-attrs/cattrs#303) &lt;303 &lt;https://github.com/python-attrs/cattrs/pull/303&gt;</code></em>)</li>
</ul>
<h2>22.1.0 (2022-04-03)</h2>
<ul>
<li>cattrs now uses the CalVer versioning convention.</li>
<li>cattrs now has a detailed validation mode, which is enabled by default. Learn more <code>here &lt;https://cattrs.readthedocs.io/en/latest/validation.html&gt;</code>_.
The old behavior can be restored by creating the converter with <code>detailed_validation=False</code>.</li>
<li><code>attrs</code> and dataclass structuring is now ~25% faster.</li>
<li>Fix an issue structuring bare <code>typing.List</code> s on Pythons lower than 3.9.
(<code>[#209](python-attrs/cattrs#209) &lt;https://github.com/python-attrs/cattrs/issues/209&gt;</code>_)</li>
<li>Fix structuring of non-parametrized containers like <code>list/dict/...</code> on Pythons lower than 3.9.
(<code>[#218](python-attrs/cattrs#218) &lt;https://github.com/python-attrs/cattrs/issues/218&gt;</code>_)</li>
<li>Fix structuring bare <code>typing.Tuple</code> on Pythons lower than 3.9.
(<code>[#218](python-attrs/cattrs#218) &lt;https://github.com/python-attrs/cattrs/issues/218&gt;</code>_)</li>
<li>Fix a wrong <code>AttributeError</code> of an missing <code>__parameters__</code> attribute. This could happen
when inheriting certain generic classes – for example <code>typing.*</code> classes are affected.
(<code>[#217](python-attrs/cattrs#217) &lt;https://github.com/python-attrs/cattrs/issues/217&gt;</code>_)</li>
<li>Fix structuring of <code>enum.Enum</code> instances in <code>typing.Literal</code> types.
(<code>[#231](python-attrs/cattrs#231) &lt;https://github.com/python-attrs/cattrs/pull/231&gt;</code>_)</li>
<li>Fix unstructuring all tuples - unannotated, variable-length, homogenous and heterogenous - to <code>list</code>.
(<code>[#226](python-attrs/cattrs#226) &lt;https://github.com/python-attrs/cattrs/issues/226&gt;</code>_)</li>
<li>For <code>forbid_extra_keys</code> raise custom <code>ForbiddenExtraKeyError</code> instead of generic <code>Exception</code>.
(<code>[#225](python-attrs/cattrs#225) &lt;https://github.com/python-attrs/cattrs/pull/225&gt;</code>_)</li>
<li>All preconf converters now support <code>loads</code> and <code>dumps</code> directly. See an example <code>here &lt;https://cattrs.readthedocs.io/en/latest/preconf.html&gt;</code>_.</li>
</ul>

</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/python-attrs/cattrs/commit/405f0291b958ae9eb45ee38febeb91fb65dd644f"><code>405f029</code></a> v22.2.0</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/89de04f57aa774d6abfb0ae62517dc8a8064e3c2"><code>89de04f</code></a> Fix some mor</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/0abbf271461babca203862f3581c20743f6118e0"><code>0abbf27</code></a> Fix tests</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/3b750439aec826a8fd20976ca113f30a27e75408"><code>3b75043</code></a> <strong>notes</strong> is list[str]</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/906b95cfef4903e2d6247abf0fdd72f7da21617a"><code>906b95c</code></a> Reorder HISTORY</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/ed7f86a0ccd9adeab895b9afac2dea69fa02bcff"><code>ed7f86a</code></a> Improve NewTypes (<a href="https://github-redirect.dependabot.com/python-attrs/cattrs/issues/310">#310</a>)</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/e7926599ad44e07d8325ae4072626e1a24705542"><code>e792659</code></a> Fix missing imports of preconf converters (<a href="https://github-redirect.dependabot.com/python-attrs/cattrs/issues/309">#309</a>)</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/e425d6378aa8dfc74bbdd9e152365e1b962fd8cf"><code>e425d63</code></a> Reorder HISTORY</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/cc56b2b873852a4e91b16706a39da00755c87759"><code>cc56b2b</code></a> Remove spurious type comment</li>
<li><a href="https://github.com/python-attrs/cattrs/commit/cbd6f29d2c0ebc40805b3ca0d81accfc330eb10c"><code>cbd6f29</code></a> Reformat</li>
<li>Additional commits viewable in <a href="https://github.com/python-attrs/cattrs/compare/v1.8.0...v22.2.0">compare view</a></li>
</ul>
</details>
<br />


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