#首字母相同的男生女生

 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]]])

 #斐波那契数列

 def fibs(num):

     result = [1, 2]

     for i in range(num - 2):

         result.append(result[-2] + result[-1])

     return result

 print(fibs(20))

 #存储全名的字典

 def init(data):

     data['first'] = {}

     data['middle'] = {}

     data['last'] = {}

 def lookup(data, label, name):

     return data[label].get(name)

 def store(data, full_name):

     names = full_name.split()

     if len(names) == 2:

         names.insert(1, ' ')

     labels = ('first', 'middle', 'last')

     for label, name = zip(labels, names):

         people = lookup(data, label, name)

         if people:

             people.append(full_name)

         else:

             data[label][name] = [full_name]

 #递归经典：阶乘、幂、二分查找

 def search(sequence, number, lower, upper):

     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)

 #模拟实现无穷算术序列

 def checkIndex(key):

     if not isinstance(key, (int, long)):

         raise TypeError

     if key < 0:

         raise IndexError

 class ArithmeticSequence:

     def __init__(self, start = 0, step = 1):

         self.start = start

         self.step = step

         self.changed = {}

     def __getitem__(self, key):

         checkIndex(key)

         try:

             return self.changed[key]

         except KeyError:

             return self.start + key * self.step

     def __setitem__(self, key, value):

         checkIndex(key)

         self.changed[key] = value

 #基本的序列与映射规则

 def checkIndex(key):

     if not isinstance(key, (int, long)):

         raise TypeError

     if key < 0:

         raise IndexError

 class ArithmeticSequence:

     def __init__(self, start = 0, step = 1):

         self.start = start

         self.step = step

         self.changed = {}

     def __getitem__(self, key):

         checkIndex(key)

         try:

             return self.changed[key]

         except KeyError:

             return self.start + key * self.step

     def __setitem__(self, key, value):

         checkIndex(key)

         self.changed[key] = value

 #带有访问计数的列表

 class CounterList(list):

     def __init__(self, *agrs):

         super(CounterList, self).__init__(*args)

         self.counter = 0

     def __getitem__(self, index):

         self.counter += 1

         return super(CounterList, self).__getitem__(index)