Fix error in basic example with Python API
Fix error in basic example with Python API

samuelshaner/openmc,johnnyliu27/openmc,liangjg/openmc,wbinventor/openmc,shikhar413/openmc,johnnyliu27/openmc,samuelshaner/openmc,wbinventor/openmc,paulromano/openmc,kellyrowland/openmc,johnnyliu27/openmc,paulromano/openmc,paulromano/openmc,bhermanmit/openmc,smharper/openmc,kellyrowland/openmc,liangjg/openmc,shikhar413/openmc,mit-crpg/openmc,smharper/openmc,walshjon/openmc,mit-crpg/openmc,johnnyliu27/openmc,walshjon/openmc,mit-crpg/openmc,lilulu/openmc,amandalund/openmc,amandalund/openmc,mit-crpg/openmc,bhermanmit/openmc,liangjg/openmc,mjlong/openmc,walshjon/openmc,amandalund/openmc,lilulu/openmc,lilulu/openmc,samuelshaner/openmc,shikhar413/openmc,walshjon/openmc,wbinventor/openmc,shikhar413/openmc,wbinventor/openmc,amandalund/openmc,liangjg/openmc,paulromano/openmc,mjlong/openmc,smharper/openmc,smharper/openmc,samuelshaner/openmc