Source: 📖 Effective Python item 14

Tuples are sorted left to right

When tuples are being compared for sorting, they are sorted by comparing items in order of index value—from left to right.

me = (1995, 'juan')			# year then name
pupi = (1991, 'victoria')	# year then name

both = [me, pupi]

year_order = both.sort()

print(year_order)	# smallest year first (1991)

>>>
[(1991, 'victoria'), (1995, 'juan')]

me = ('juan', 1995)			# name then year
pupi = ('vicotira, 1991')	# name then year

both = [me, pupi]

year_order = both.sort()

print(year_order)	# 'smallest' name first ('juan')

>>>
[('juan', 1995), ('victoria', 1991)]

In the top example, the sort function looks at the year first as it's at the first index position of the tuple, and compares to find the smallest value. 1991 < 1995, so the pupi object is sorted before the me object.

In the second example, the sort function looks at the name first as it's at the first index position of the tuple, and compares to find the smallest value. 'juan' is alphabetically lesser than 'victoria', so the me object is sorted before the pupi object.