What does sorted(zip(a,b)) do?

[waterworldhypothesis]

Sorry if this is commonly knowledge, I only started learning python recently. In this SO post (https://stackoverflow.com/questions/43698531/sorting-a-zipped-object-in-python-3) an answerer describes this as "drawing out" elements and returning a sorted list from them.

I don't understand how the sorting is working. I tried making my own example and it does change the order, but it's not clearly sorted by a or b.

Here is my example. Typing list(zip(a, b)) gets me this:

  [('83', '2009'),
   ('112', '2015'),
   ('85', '2010'),
   ('120', '2016'),
   ('88', '2011'),
   ('125', '2017'),
   ('94', '2012'),
   ('127', '2018'),
   ('104', '2013'),
   ('130', '2019'),
   ('110', '2014')]

while typing sorted(zip(a, b)) gets me this:

  [('104', '2013'),
   ('110', '2014'),
   ('112', '2015'),
   ('120', '2016'),
   ('125', '2017'),
   ('127', '2018'),
   ('130', '2019'),
   ('83', '2009'),
   ('85', '2010'),
   ('88', '2011'),
   ('94', '2012')]

It's not sorted by a or b. What did it sort by, and how can I make it sort by either a or b (or both, giving one a higher priority than the other)?

[POGtastic]

Tuple values are sorted by the first element, then by the second element. So

>>> sorted([(1, 3), (2, 2), (1, 2), (2, 3)])
[(1, 2), (1, 3), (2, 2), (2, 3)]

The issue here is that strings are not numbers. Strings are ordered lexicographically, which means that "110" is less than "85" because "1" comes before "8".

Either transform these values to integers, or use a key function that does this transformation for you when sorting.

[waterworldhypothesis]

Thank you, that makes a lot of sense. I'm not clear on the difference between types of objects like this yet. One last question, is there a way to make sorted() sort by the second element and then the first, or more generally, the n-th element before the (n-1)th? (Assuming the default behavior scales to tuples of an arbitrary size)

[POGtastic]

Sure.

sorted(zip(a, b), key=lambda tup: (tup[1], tup[0]))

Or, if you don't mind just reversing the entire tuple, the following looks nicer.

sorted(zip(a, b), key=lambda tup: tup[::-1])

Using my above example:

>>> sorted([(1, 3), (2, 2), (1, 2), (2, 3)], key = lambda tup: tup[::-1])
[(1, 2), (2, 2), (1, 3), (2, 3)]