Helpful note when union may not have been narrowed

[dexterkennedy]

Fixes #17036

The added note makes it easier for new mypy users to understand where the errors are coming from and suggests a potentially simple fix.

[github-actions]

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

pip (https://github.com/pypa/pip)
+ src/pip/_internal/metadata/pkg_resources.py:162: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/network/utils.py:63: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/network/utils.py:93: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/network/auth.py:520: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/network/auth.py:543: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/network/session.py:408: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/index/collector.py:87: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/cli/req_command.py:151: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/pip/_internal/cli/req_command.py:152: note: You can use "if <variable_name> is not None" to protect against a None value

check-jsonschema (https://github.com/python-jsonschema/check-jsonschema)
+ src/check_jsonschema/cli/param_types.py:90: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/check_jsonschema/cli/param_types.py:91: note: You can use "if <variable_name> is not None" to protect against a None value

dragonchain (https://github.com/dragonchain/dragonchain)
+ dragonchain/broadcast_processor/broadcast_functions.py:95:32: note: You can use "if <variable_name> is not None" to protect against a None value
+ dragonchain/lib/authorization.py:315:19: note: You can use "if <variable_name> is not None" to protect against a None value
+ dragonchain/lib/authorization.py:317:25: note: You can use "if <variable_name> is not None" to protect against a None value
+ dragonchain/lib/authorization.py:340:31: note: You can use "if <variable_name> is not None" to protect against a None value

steam.py (https://github.com/Gobot1234/steam.py)
+ steam/id.py:558: note: You can use "if <variable_name> is not None" to protect against a None value

prefect (https://github.com/PrefectHQ/prefect)
+ src/prefect/utilities/dispatch.py:183: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/collections.py:188: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/server/utilities/server.py:24: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/server/utilities/database.py:632: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/_internal/concurrency/services.py:190: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/_internal/concurrency/services.py:195: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/importtools.py:162: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/importtools.py:338: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/importtools.py:339: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/_internal/compatibility/deprecated.py:344: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/client/schemas/objects.py:359: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/events/related.py:121: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/events/related.py:129: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/events/related.py:132: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/events/related.py:140: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/events/related.py:143: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/events/related.py:151: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/events/related.py:154: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/client/base.py:287: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/blocks/core.py:71: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/filesystems.py:716: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runner/storage.py:298: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/runner.py:421: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/runner.py:967: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/runner.py:972: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/runner.py:976: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/runner.py:988: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/runner.py:992: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/runner.py:996: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/logging/handlers.py:203: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/flow_run.py:124: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/flow_run.py:143: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/flow_run.py:158: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/flow_run.py:173: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/flow_run.py:188: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/flow_run.py:203: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/flow_run.py:226: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:135: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:154: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:390: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:391: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:392: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:393: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:400: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/utilities/engine.py:494: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/deployment.py:109: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runtime/deployment.py:110: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runner/submit.py:68: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/runner/submit.py:206: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/input/run_input.py:117: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:159: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:161: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:178: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:192: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:194: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:199: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:201: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:212: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:231: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:529: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/deployments.py:800: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/base.py:112: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/base.py:124: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/base.py:136: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/deployments/base.py:149: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:620: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:630: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:642: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:643: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:680: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:797: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:862: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:885: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:907: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:915: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:937: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:1132: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:1172: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:1327: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:1337: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/prefect/engine.py:1357: note: You can use "if <variable_name> is not None" to protect against a None value

... (truncated 165 lines) ...

aioredis (https://github.com/aio-libs/aioredis)
+ aioredis/connection.py:934: note: You can use "if <variable_name> is not None" to protect against a None value

Tanjun (https://github.com/FasterSpeeding/Tanjun)
+ tanjun/dependencies/limiters.py:819: note: You can use "if <variable_name> is not None" to protect against a None value

sphinx (https://github.com/sphinx-doc/sphinx)
+ sphinx/builders/html/__init__.py:441:16: note: You can use "if <variable_name> is not None" to protect against a None value

pytest (https://github.com/pytest-dev/pytest)
+ src/_pytest/_code/code.py:1077: note: You can use "if <variable_name> is not None" to protect against a None value
+ src/_pytest/_code/code.py:1083: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:858: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:861: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:912: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:914: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:923: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:924: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:929: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:940: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:1281: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:1283: note: You can use "if <variable_name> is not None" to protect against a None value
+ testing/_py/test_local.py:1284: note: You can use "if <variable_name> is not None" to protect against a None value

operator (https://github.com/canonical/operator)
+ ops/lib/__init__.py:263: note: You can use "if <variable_name> is not None" to protect against a None value

kornia (https://github.com/kornia/kornia)
+ kornia/enhance/histogram.py:217: note: You can use "if <variable_name> is not None" to protect against a None value
+ kornia/enhance/histogram.py:220: note: You can use "if <variable_name> is not None" to protect against a None value
+ kornia/enhance/histogram.py:241: note: You can use "if <variable_name> is not None" to protect against a None value
+ kornia/enhance/histogram.py:244: note: You can use "if <variable_name> is not None" to protect against a None value
+ kornia/enhance/histogram.py:249: note: You can use "if <variable_name> is not None" to protect against a None value
+ kornia/enhance/histogram.py:251: note: You can use "if <variable_name> is not None" to protect against a None value

werkzeug (https://github.com/pallets/werkzeug)
+ tests/test_wrappers.py:179: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_wrappers.py:180: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_wrappers.py:181: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_wrappers.py:189: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_wrappers.py:190: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_wrappers.py:191: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_wrappers.py:1078: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_wrappers.py:1081: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_test.py:166: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_test.py:168: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_test.py:306: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_test.py:307: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_routing.py:601: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_routing.py:603: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_routing.py:1310: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_local.py:191: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:152: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:153: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:154: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:157: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:158: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:159: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:162: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:163: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:164: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:176: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:177: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:178: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:179: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:180: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:181: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:182: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:183: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:184: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:185: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:195: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:196: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:197: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:198: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:199: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:200: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:201: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:205: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:211: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:212: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:217: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:218: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:242: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:243: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:244: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:245: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:253: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:254: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:255: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:256: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:257: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:259: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:266: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:267: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:272: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:273: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:623: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:624: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:625: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:628: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:629: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:630: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:633: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:634: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:635: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:638: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:639: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:640: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:643: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:644: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:645: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:664: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:665: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:666: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:667: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:668: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:677: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:678: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:679: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:680: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:681: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:684: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:685: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:686: note: You can use "if <variable_name> is not None" to protect against a None value
+ tests/test_http.py:687: note: You can use "if <variable_name> is not None" to protect against a None value

... (truncated 4 lines) ...

discord.py (https://github.com/Rapptz/discord.py)
+ discord/mentions.py:126: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/mentions.py:131: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/invite.py:460: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/guild.py:3232: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/app_commands/commands.py:225: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/app_commands/commands.py:661: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/app_commands/commands.py:662: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/app_commands/commands.py:2381: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/app_commands/commands.py:2383: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/ext/commands/core.py:430: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/ext/commands/core.py:438: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/ext/commands/core.py:451: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/ext/commands/core.py:468: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/ext/commands/core.py:476: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/ext/commands/hybrid.py:309: note: You can use "if <variable_name> is not None" to protect against a None value
+ discord/ext/commands/hybrid.py:319: note: You can use "if <variable_name> is not None" to protect against a None value

streamlit (https://github.com/streamlit/streamlit)
+ lib/tests/streamlit/streamlit_test.py:61:30: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/scriptrunner/script_requests_test.py:116:32: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/scriptrunner/script_requests_test.py:119:31: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/scriptrunner/script_requests_test.py:141:32: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/scriptrunner/script_requests_test.py:142:31: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/scriptrunner/script_requests_test.py:163:32: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/scriptrunner/script_requests_test.py:164:31: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/logger_test.py:104:21: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/logger_test.py:108:21: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/config_test.py:402:23: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:136:27: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:139:9: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:145:9: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:146:9: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:153:9: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:154:9: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:163:16: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:165:16: note: You can use "if <variable_name> is not None" to protect against a None value
+ lib/tests/streamlit/runtime/websocket_session_manager_test.py:168:16: note: You can use "if <variable_name> is not None" to protect against a None value

... (truncated 108 lines) ...```

[hauntsaninja]

Thanks for the PR! We should scope the new hint to only the case where None is in the union

[dexterkennedy]

Thanks for the PR! We should scope the new hint to only the case where None is in the union

I was working on scoping the error message to only show up when None is in the union and when an attribute of a None type object is accessed.

This is the if statement I used to determine whether to show the note:

if typ_format == '"None"' and "None" in orig_type_format:
self.note(
'You can use "if <variable_name> is not None" to protect against a None value',
context,
code=codes.UNION_ATTR,
)

However when trying to do so I tested individual test cases, which appeared to be entering the if statement and providing the note correctly. So I ran the entire test suite using "python3 runtests.py" and based on the results, the tests seem to never enter into the if statement and print out the note.

This has been very confusing and I am wondering why this is occurring and if I am missing something. Any help/guidance is appreciated. Thanks.