How can I compare two strings case-insensitively?

[Jameshsia7]

Vyper: 0.4.0
Python: 3.11
OS: Windows 10

I'm trying to compare two strings in a case-insensitive way. In Python, the code would be:
if a.lower() == b.lower():

How can I do the equivalent in Vyper?

If I try it, I get:

vyper.exceptions.StructureException: String[255] instance does not have members

Thank you