python 列表推导式

>>> [x*x for x in range(10)]
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
>>> [x*x for x in range(10) if x % 3 == 0]
[0, 9, 36, 81]
>>> [ (x,y) for x in range(3) for y in range(3)]
[(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2, 1), (2, 2)]

 

 

girls = ['alice', 'bernice', 'clarice', 'aaaa']
boys = ['chris', 'arnold', 'bob']
letterGirls = {}

for gril in girls:
    letterGirls.setdefault(gril[0],[]).append(gril)

print(letterGirls)

print([b + '+' + g for b in boys for g in letterGirls[b[0]]])

result:

{'a': ['alice', 'aaaa'], 'b': ['bernice'], 'c': ['clarice']}
['chris+clarice', 'arnold+alice', 'arnold+aaaa', 'bob+bernice']