#!/bin/env python
# From: https://docs.python.org/3/tutorial/controlflow.html#lambda-expressions

# This uses lambda expressions to specify how to sort a list of pairs:
pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
pairs.sort(key=lambda pair: pair[0])
#              ^^^^^^^^^^^^^^^^^^^^ a function that extracts the key, ie. sort by 1st elem (numerically)
print(pairs)
# this should print
# [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
pairs.sort(key=lambda pair: pair[1])
#              ^^^^^^^^^^^^^^^^^^^^ a function that extracts the key, ie. sort by 2nd elem (lexico.)
print(pairs)
# this should print
# [(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]