Traceback (most recent call last): File "", line 1, in NameError: name 'sheet' is ...
Thiserrormessageisindicatingthatthereisnovariableorobjectdefinedinthecurrentscopewiththename"sheet".Thiscouldhappenifyouaretryingtoaccessormanipulateavariablethathasnotbeendefinedinyourcodeorhasgoneou