The sooner one starts using safety nets like strictures, lexically scoped variables, full error messages and so on the more benefit one derives from their use and the more likely that such techniques will become habit. The time when such techniques are most useful is during the discovery stages of learning the language, not later on when one should know better in any case and has a better debugging toolkit to help sort problems out in any case.

While there is a balance between introducing too much and introducing good habits early, the OP (by accident or design) is already using strictures and checking the success of open, so introducing another related three safety net techniques seems reasonable.