Adds decorated @property support, refs #1362

[sobolevn]

This is not fully ready right now, but looks like the first test passes 🎉

Closes #1362

[sobolevn]

Things TODO:

• Ensure that @property is the last (the top-most) decorator in chain. This is a slight limitation we have, but this I cannot think of use-cases when this is used differently
• Add support for decorated @property.setter
• @final @property support
• Add better error message for @overload and @property used together. I don't plan to support this feature in this PR, but I guess overloded properties can be a thing later, since we can have different self types

[sobolevn]

Friendly ping to @unparalleled-js. You offered your help, so maybe you would have some time to review my code 🙂

[antazoey]

I tested it out for both @property and @cached_property and ran mypy and some other projects, as a manual regression.

I am not sure about the other test failures yet but I can keep diving in, this is my first time peaking around mypy but I am invested.

[sobolevn]

I tested it out for both @Property and @cached_property and ran mypy and some other projects, as a manual regression.

Thank you! Any interesting finds? 🙂

I am not sure about the other test failures

Test failures are about incorrect test fixture and explicit Any in it. I will fix it later today. It is not related to the feature itself (I hope).

this is my first time peaking around mypy but I am invested.

🚀 👍

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

twine (https://github.com/pypa/twine)
+ twine/auth.py:32: error: Unused "type: ignore" comment
+ twine/auth.py:42: error: Unused "type: ignore" comment

steam.py (https://github.com/Gobot1234/steam.py)
+ steam/ext/commands/converters.py:277: error: Property must be used as the top-most decorator  [misc]

kopf (https://github.com/nolar/kopf)
+ kopf/_core/actions/invocation.py:59: error: Property must be used as the top-most decorator
+ kopf/_core/actions/invocation.py:64: error: Property must be used as the top-most decorator
+ kopf/_core/actions/invocation.py:69: error: Property must be used as the top-most decorator

core (https://github.com/home-assistant/core)
+ homeassistant/components/sensor/__init__.py:300: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/sensor/__init__.py:341: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/sensor/__init__.py:359: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/light/__init__.py:882: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/vacuum/__init__.py:294: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/switch/__init__.py:133: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/siren/__init__.py:156: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/remote/__init__.py:175: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/lock/__init__.py:160: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/lock/__init__.py:170: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/image_processing/__init__.py:179: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/geo_location/__init__.py:84: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/fan/__init__.py:462: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/device_tracker/legacy.py:686: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/device_tracker/config_entry.py:124: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/device_tracker/config_entry.py:168: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/cover/__init__.py:245: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/calendar/__init__.py:145: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/binary_sensor/__init__.py:202: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/alarm_control_panel/__init__.py:212: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/air_quality/__init__.py:134: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/weather/__init__.py:205: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/water_heater/__init__.py:163: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/water_heater/__init__.py:197: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/norway_air/air_quality.py:99: error: Unused "type: ignore" comment
+ homeassistant/components/norway_air/air_quality.py:105: error: Unused "type: ignore" comment
+ homeassistant/components/norway_air/air_quality.py:111: error: Unused "type: ignore" comment
+ homeassistant/components/norway_air/air_quality.py:117: error: Unused "type: ignore" comment
+ homeassistant/components/norway_air/air_quality.py:123: error: Unused "type: ignore" comment
+ homeassistant/components/media_player/__init__.py:920: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/climate/__init__.py:254: error: Property must be used as the top-most decorator  [misc]
+ homeassistant/components/camera/__init__.py:574: error: Property must be used as the top-most decorator  [misc]

scikit-learn (https://github.com/scikit-learn/scikit-learn)
+ sklearn/utils/tests/test_deprecation.py:23: error: Property must be used as the top-most decorator
+ sklearn/preprocessing/_polynomial.py:495: error: Property must be used as the top-most decorator
+ sklearn/preprocessing/_data.py:2270: error: Property must be used as the top-most decorator
+ sklearn/svm/_base.py:129: error: Property must be used as the top-most decorator
+ sklearn/decomposition/_kernel_pca.py:283: error: Property must be used as the top-most decorator
+ sklearn/decomposition/_kernel_pca.py:293: error: Property must be used as the top-most decorator
+ sklearn/decomposition/_kernel_pca.py:302: error: Property must be used as the top-most decorator
+ sklearn/cluster/_kmeans.py:1740: error: Property must be used as the top-most decorator
+ sklearn/cluster/_kmeans.py:1748: error: Property must be used as the top-most decorator
+ sklearn/cluster/_kmeans.py:1756: error: Property must be used as the top-most decorator
+ sklearn/neighbors/_base.py:588: error: Property must be used as the top-most decorator
+ sklearn/manifold/_mds.py:460: error: Property must be used as the top-most decorator
+ sklearn/cluster/_affinity_propagation.py:425: error: Property must be used as the top-most decorator
+ sklearn/neighbors/_regression.py:188: error: Property must be used as the top-most decorator
+ sklearn/model_selection/_search.py:420: error: Property must be used as the top-most decorator
+ sklearn/covariance/_graph_lasso.py:1017: error: Property must be used as the top-most decorator
+ sklearn/covariance/_graph_lasso.py:1037: error: Property must be used as the top-most decorator
+ sklearn/manifold/_spectral_embedding.py:541: error: Property must be used as the top-most decorator
+ sklearn/cluster/_spectral.py:740: error: Property must be used as the top-most decorator
+ sklearn/cluster/_birch.py:485: error: Property must be used as the top-most decorator
+ sklearn/cluster/_birch.py:494: error: Property must be used as the top-most decorator
+ sklearn/pipeline.py:728: error: Property must be used as the top-most decorator
+ sklearn/naive_bayes.py:500: error: Property must be used as the top-most decorator
+ sklearn/naive_bayes.py:705: error: Property must be used as the top-most decorator
+ sklearn/naive_bayes.py:718: error: Property must be used as the top-most decorator
+ sklearn/naive_bayes.py:735: error: Property must be used as the top-most decorator
+ sklearn/multiclass.py:554: error: Property must be used as the top-most decorator
+ sklearn/multiclass.py:573: error: Property must be used as the top-most decorator
+ sklearn/multiclass.py:586: error: Property must be used as the top-most decorator
+ sklearn/multiclass.py:905: error: Property must be used as the top-most decorator
+ sklearn/kernel_ridge.py:166: error: Property must be used as the top-most decorator
+ sklearn/dummy.py:458: error: Property must be used as the top-most decorator
+ sklearn/dummy.py:705: error: Property must be used as the top-most decorator
+ sklearn/tree/_classes.py:1005: error: Property must be used as the top-most decorator
+ sklearn/tree/_classes.py:1325: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:504: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:512: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:520: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:528: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:536: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:1090: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:1100: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:1108: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:1116: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:1124: error: Property must be used as the top-most decorator
+ sklearn/cross_decomposition/_pls.py:1132: error: Property must be used as the top-most decorator
+ sklearn/feature_selection/_rfe.py:758: error: Property must be used as the top-most decorator
+ sklearn/ensemble/_forest.py:648: error: Property must be used as the top-most decorator
+ sklearn/ensemble/_bagging.py:471: error: Property must be used as the top-most decorator
+ sklearn/ensemble/_gb.py:895: error: Property must be used as the top-most decorator
+ sklearn/ensemble/_gb.py:1933: error: Property must be used as the top-most decorator

pandas (https://github.com/pandas-dev/pandas)
+ pandas/core/base.py:198: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/base.py:214: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/base.py:219: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/indexes/base.py:841: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/indexes/base.py:2096: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/indexes/base.py:2138: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/indexes/base.py:2156: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/indexes/base.py:2181: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/indexes/base.py:2566: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/indexes/base.py:4720: error: Unused "type: ignore" comment
+ pandas/core/indexes/base.py:6831: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/arrays/interval.py:1394: error: Unused "type: ignore" comment
+ pandas/core/indexes/numeric.py:272: error: Unused "type: ignore" comment
+ pandas/core/indexes/period.py:182: error: Unused "type: ignore" comment
+ pandas/core/indexes/period.py:189: error: Unused "type: ignore" comment
+ pandas/core/indexes/period.py:196: error: Unused "type: ignore" comment
+ pandas/core/internals/base.py:159: error: Property must be used as the top-most decorator  [misc]
+ pandas/io/parsers/base_parser.py:314: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/series.py:721: error: Unused "type: ignore" comment
+ pandas/core/series.py:722: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/generic.py:350: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/generic.py:472: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/generic.py:4095: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/generic.py:5640: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/internals/blocks.py:165: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/internals/blocks.py:177: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/internals/blocks.py:188: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/internals/blocks.py:200: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/internals/blocks.py:237: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/grouper.py:301: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/grouper.py:419: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/groupby.py:597: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/groupby.py:605: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/groupby.py:610: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/groupby.py:676: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/groupby.py:1735: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/ops.py:735: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/ops.py:792: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/ops.py:827: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/ops.py:842: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/ops.py:865: error: Property must be used as the top-most decorator  [misc]
+ pandas/core/groupby/ops.py:876: error: Property must be used as the top-most decorator  [misc]

[sobolevn]

Ok, I have to admit that my .property_decorator hack didn't work. We have too many possible decorators that can go on top: @final, @no_type_check, @custom_cache, @abtract, etc.

Fixing one problem and introducing another one is not ideal.

---

New plan: @property is just a regular descriptor with __get__ and __set__ methods. I guess I should concentrate on making it work as it should.