Import files in Nexus format can be done by the viewer, which also opens a dialog allowing to browse into the file to select the data location.

https://github.com/vais-ral/CILViewer/blob/c33ace9a01601a29c30dc7ec9c266ae5cc1e1b73/Wrappers/Python/ccpi/viewer/ui/dialogs.py#L142