AttributeError: 'generator' object has no attribute 'next'

This error occurs when you are trying to access the next element of a generator object using the `.next()` method which does not exist in Python 3.x. Instead, you should use the built-in `next()` function.

For example, if you have a generator object `gen` and you want to access the next element, you should use:

next(gen)

This will return the next element of the generator object.