[Bug]: non-required dependency typing_extensions is imported by default

[arjxn-py]

PyBaMM Version

24.1

Python Version

3.8-3.12

Describe the bug

There might be some instance in #3578 where non required dependency has been imported by default, which is causing failure, related build logs.

Steps to Reproduce

• try installing latest built wheels on develop
• do import pybamm

Relevant log output

No response

[agriyakhetarpal]

Note: this happens with sympy as well

[agriyakhetarpal]

Also, it's weird that the tests for have_optional_dependency in test_util.py didn't catch typing-extensions and sympy – is this because we are not mocking all of the optional dependencies inside that test case? IMO, we should mock all of the optional dependencies to ensure that this problem doesn't get repeated in the future.

[arjxn-py]

I tried importing typing-extensions as an optional dependency but it is being imported outside a function in unit/type_definitions.py and then those types in type_definitions.py are then being imported and used as args at several instances, which is making have_optional_dependency unable to resolve the issue.

[arjxn-py]

How about we consider making typing-extensions a required dependency?

[agriyakhetarpal]

I see, making typing-extensions a required dependency should be okay (please update the table in the docs too, of course). Will sympy still remain optional?