# \[issue\] platform not defined

**URL:** <https://cylc.discourse.group/t/issue-platform-not-defined/1285>\
**Category:** Cylc Support\
**Created:** [January 30, 2026, 2:31am UTC](https://cylc.discourse.group/t/issue-platform-not-defined/1285 "2026-01-30T02:31:37Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![oliver.sanders](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/oliver.sanders/32/110_2.png) [@oliver.sanders](https://cylc.discourse.group/u/oliver.sanders)\
**Post date:** [February 2, 2026, 9:28am UTC](https://cylc.discourse.group/t/issue-platform-not-defined/1285/9 "2026-02-02T09:28:58Z")

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Hi,

Yes, we clear the `PYTHONPATH` argument as this often causes conflicts between the Cylc/Rose environment and the job environment ([context](https://cylc.discourse.group/t/rose-pythonpath/862)).

If you need to add a module into the Cylc/Rose environment’s Python path (and not the job environment’s Python path), use the [`CYLC_PYTHONPATH`](https://cylc.github.io/cylc-doc/stable/html/reference/changes.html#cylc-ignores-pythonpath) and `ROSE_PYTHONPATH` variables.

However, this isn’t necessary for normal installations, it’s only required if things have been installed into non-standard locations so `PYTHONPATH` is needed to locate them.

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_[View the full topic](https://cylc.discourse.group/t/issue-platform-not-defined/1285)._