xlwings code:

#Referencing Cells Using Variables

import xlwings as xw    #Import the xlwings package

app=xw.App()
bk=app.books.active    #Get the active workbook
sht=bk.sheets.active    #Get the active worksheet

#xlwings
i=3    #Create a variable `i`
sht.range("C"+ str(i)).select()    #Reference a cell using the variable `i`
#sht.cells(i,i).select()

#xlwings API
#i=3
#sht.api.Range("C"+ str(i)).Select()
#sht.api.Cells(i,i).Select()

#bk.close()
#app.kill()