# Problems with TypeIs

**URL:** <https://discuss.python.org/t/problems-with-typeis/55410>\
**Category:** Typing\
**Tags:** typing\
**Created:** [June 10, 2024, 5:46pm UTC](https://discuss.python.org/t/problems-with-typeis/55410 "2024-06-10T17:46:45Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![mikeshardmind](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/mikeshardmind/32/14381_2.png) [@mikeshardmind](https://discuss.python.org/u/mikeshardmind)\
**Post date:** [June 10, 2024, 6:07pm UTC](https://discuss.python.org/t/problems-with-typeis/55410/2 "2024-06-10T18:07:16Z")

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The negation problem isn’t clearly shown by this example, I did recently edit the referenced post to have a negation example with structural types. Structural types don’t play nicely with TypeIs at all here though, this also has a bad interaction with use of a structural type to erase variance (that this example does show), something which is common with list vs Sequence with how people write code.

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