Second wild idea of the day:
The dict constructor currently accepts sequences where each element has length 2, interpreted as a key-value pair.
Let's have it also accept sequences with elements of length 1, interpreted as a key:None pair.
The benefit is that it provides a way to rapidly construct sets:
lowercase = dict('abcdefghijklmnopqrstuvwxyz') if char in lowercase: ...
dict([key1, key2, key3, key1]).keys() # eliminate duplicate keys
Raymond Hettinger 'regnitteh dnomyar'[::-1]