Beginning Python: From Novice to Professional, Second Edition

中文版p83页：

girls = ['alice', 'bernice', 'clarice']
boys = ['chris', 'arnold', 'bob']
letterGirls = {}
for girl in girls:
    letterGirls.setdefault(girl[0], []).append(girl)
print ([b+'+'+g for b in boys for g in letterGirls[b[0]]])

输出结果：

>>>
['chris+clarice', 'arnold+alice', 'bob+bernice']

原理：

>>> girls = ['alice', 'bernice', 'clarice']
>>> letterGirls = {}
>>> for girl in girls:
 letterGirls.setdefault(girl[0], []).append(girl)

 
>>> print letterGirls
{'a': ['alice'], 'c': ['clarice'], 'b': ['bernice']}

letterGirls.setdefault(girl[0], [])

'a':[] 

 letterGirls.setdefault(girl[0], []).append(girl)

'a':['alice']

如此便是个很好的方法。

p91：

斐波那契数列：

def fibs(num):
    result = [0, 1]
    for i in range(num-2):
        result.append(result[-2] + result[-1])
    return result
num = input('How many Fibonacci numbers do you want? ')
print fibs(num)