Accept iterable sequence and return them in reverse order

Question

Write a generator function reverse_iter that accepts an iterable sequence and yields the items in reverse order without using built-in functions or methods. After using the function however, the original list should be unchanged. An example output is below:

   it = reverse_iter(nums)
    next(it) == 4
True
    next(it)
3
    next(it)
2
    next(it)
1

Note that the above should work even if the list is changed to a tuple. I have no idea how to do this without using something like reverse() or reversed(). Maybe utilize a -1 slice? Any Ideas?

I cannot use built-in functions which would automatically reverse the list and others such as that. I think there might be a way to implement something like a slice? Not sure though. — user10019227, Aug 07 '18 at 04:45
So you just need to yield `nums[-1]`, `nums[-2]`, etc. until `nums[0]`? I think it's not that hard if you try... — Jeronimo, Aug 07 '18 at 05:52

Tanmay jain · Accepted Answer · 2018-08-08T05:34:53.723

def reverse_iter(nums): # A generator function
    idx = len(nums) - 1
    while idx > -1:
        yield nums[idx]
        idx -=1 

nums = [1,2,3,4]
print('before: ',*nums)
get = reverse_iter(nums)  # get is a generator object

print('manually')
# Iterating over the generator object using next
print(get.__next__()) # In Python 3+ , print(get.__next__())
print(get.__next__())
print(get.__next__())
print(get.__next__())

#print(get.next()) #now you will get StopIteration
#print(next(get,'traversing complete')) #to avoid the StopIteration exception


# printing all items in list in reverse 
print('\nusing for loop')
get = reverse_iter(nums)  # get is a generator object
for i in range(len(nums)):
    print(get.__next__())

print('after: ',*nums)

why I am getting downvotes ? is answer incorrect ? – Tanmay jain Aug 13 '18 at 11:44 — Tanmay jain, Aug 13 '18 at 11:44

Accept iterable sequence and return them in reverse order

1 Answers1