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)

阶乘：

递归版本

def factorial(n):

　　if n == 1:

return 1

else:

return n * factorial(n-1)

非递归：

def factorial(n):

　　result = n

　　for i in range(1,n):

　　　　result *= i

return result

power函数：

递归

def power(x, n):
if n == 0:
return 1
else:
return x * power(x, n-1)

非递归

def pow(x,n):

　　result = 1

　　for i in range(n):

　　　　result *= x

　　resturn result

二分查找：

def search(sequence, number, lower=0, upper=None):
if upper is None: upper = len(sequence)-1
if lower == upper:
assert number == sequence[upper]
return upper
else:
middle = (lower + upper) // 2
if number > sequence[middle]:
return search(sequence, number, middle+1, upper)
else:
return search(sequence, number, lower, middle)