UnboundLocalError when using BIDSLayout with specific indexer

[alperkent]

Hello!

I encountered an UnboundLocalError when trying to create a BIDSLayout with a specific indexer. Here's the code snippet that produces the error:

import bids

filters = {'datatype': 'eeg', 'suffix': 'eeg'}
indexer = bids.BIDSLayoutIndexer(**filters)
layout = bids.BIDSLayout('../data/bids-examples/eeg_ds000117', indexer=indexer)

Here's the error message:

UnboundLocalError: cannot access local variable 'ext_key' where it is not associated with a value

The error occurs in the following lines of the PyBIDS package:

layout.py:177, in BIDSLayout.__init__
index.py:154, in BIDSLayoutIndexer.__call__
index.py:268, in BIDSLayoutIndexer._index_metadata

In the _index_metadata method, the variable ext_key is used in the if filters.get(ext_key): statement before it has been assigned a value. The error seems to occur because of this issue.

Environment:

• PyBIDS version: 0.16.4
• Python version: 3.12
• Operating System: macOS

I would appreciate any help or guidance on this issue. If you need any more information, please let me know. Thank you in advance for your time and assistance.