file ""line in indexerrorlist index out of range to see why this error happenslet' walk through the code firstthe animals list would be set to ['cat''mouse''dog''horse'and len(animalswould return this means that the call to range( would cause the for loop to iterate with the values and when the for loop iterates with set to the if statement' condition will be true and the del animals[istatement will delete animals[ this means that afterwards the animals list will be ['cat''mouse''horse'the indexes of all the items after 'dogare all shifted down by one because the 'dogvalue was removed but on the next iteration through the for loopi is set to but animals[ is out of bounds because the valid indexes of the animals list is no longer to but to the original call to range(was for list with items in it the list changed in lengthbut the for loop is set up for the original length howeverif we iterate from the last index of the list to we don' run into this problem the following program deletes the 'dogstring from the animals list without causing an indexerror erroranimals ['cat''mouse''dog''horse'for in range(len(animals - - )if animals[ ='dog'del animals[ithe reason this code doesn' cause an error is because the for loop iterates over and on the first iterationthe code checks if animals[ is equal to 'dogit isn' (animals[ is 'horse'so the code moves on to the next iteration then animals[ is checked if it equals 'dogit doesso animals[ is deleted after animals[ is deletedthe animals list is set to ['cat''mouse''horse'on the next iterationi is set to there is value at animals[ (the 'mousevalue)so no error is caused it doesn' matter that all the items in the list after 'doghave shifted down by onebecause since we started at the end of the list and are going towards the frontall of those items have already been checked similarlywe can delete grass and squirrel objects from the grassobjs and squirrelobjs lists without error because the for loop on lines and iterate in reverse order email questions to the authoral@inventwithpython com