Convert a list with strings all to lowercase or uppercase

It can be done with list comprehensions

>>> [x.lower() for x in ["A", "B", "C"]]
['a', 'b', 'c']
>>> [x.upper() for x in ["a", "b", "c"]]
['A', 'B', 'C']

or with the map function

>>> list(map(lambda x: x.lower(), ["A", "B", "C"]))
['a', 'b', 'c']
>>> list(map(lambda x: x.upper(), ["a", "b", "c"]))
['A', 'B', 'C']