@dmc5809, you could google "python sort key" to get an explanation yourself, you know?

Great solution. I am confused as to how key=weight_key is working. I see you are using the function as a keyword arg, but the function is not being executed (). Can you explain more please?

Thanks

The sorted key parameter receives a tuple from weight_key which contains two values: First the weight-value, and second the string value itself.

In your example using "11" and "20000" the keys are thus (2, "11"), and (2, "20000"). Hence the weigh-values are equal, but the string values differ and are sorted accordingly.

I hope this clarifies it.

You can find a better range than this: for i in range(2, n+1)
Google is your friend. Try "prime factors algorithm"

This is because my solution is written in Python 2, while you are using Python 3. zip() returns a list in Python 2. In Python 3, it returns ZipObject (a lazy iterator, which computes each next value only when you actually ask for it). See https://docs.python.org/3/library/functions.html#zip

Spoilers...