LGTM.com - false positive for py/uninitialized-local-variable

**Description of the false positive**

The error says that a variable may be used before it is initialized but the variable is defined on the line above. I cannot see a way that it would not be initialized.

**URL to the alert on the project page on LGTM.com**

It does not appear in LGTM.com (seems the `py/uninitialized-local-variable` alert is [hidden by default](https://lgtm.com/rules/10030097/)) but on GitHub, using the CodeQL action, it is https://github.com/rparini/cxroots/security/code-scanning/28 Apologies if this is the wrong place for this report.