python3高阶函数库functools

###python2.7中functools库wrapper,reduce,partial,total_ordering,cmp_to_key

• cmp_to_key见名知意把cmp比较函数转换成key比较函数，python3中不支持cmp;
• total_ordering 这个装饰器是在python2.7的时候加上的，它是针对某个类如果定义了lt、le、gt、ge这些方法中的至少一个，使用该装饰器，则会自动的把其他几个比较函数也实现在该类中;
• reduce 和之前的reduce函数意义相同;
• partial局部部分的意思，可以固定函数的部分参数变成定制的函数，看到有些书上翻译成偏函数感觉非常晦涩;
• wrapper 装饰器函数，把装饰器函数伪装成被装饰函数，实际调用的是update_wrapper，源码设置了name,doc,module,dict属性给装饰器函数；

python3.6.5中functools库新增了lru_cache和singledispatch

• lru_cache缓存计算结果
• singledispatch 有点类似c++中的泛型和多态

  import time
  from operator import mul
  from functools import cmp_to_key, total_ordering, reduce, partial, wraps, lru_cache, singledispatch
  
  a = [5, 6, 1, 2, 3, 4]
  
  
  def my_cmp(x, y):
      if x < y:
          return -1
      if x > y:
          return 1
      return 0
  
  print(sorted(a, key=cmp_to_key(my_cmp)))
  
  
  @total_ordering #如果去掉 >= 不能使用
  class Student:
      def __init__(self, first, last):
          self.firstname = first
          self.lastname = last
  
      def __eq__(self, other):
          return ((self.lastname.lower(), self.firstname.lower()) ==
                  (other.lastname.lower(), other.firstname.lower()))
  
      def __lt__(self, other):
          return ((self.lastname.lower(), self.firstname.lower()) <
                  (other.lastname.lower(), other.firstname.lower()))
  
  c = Student('abc', 'kevin')
  b = Student('zuang', 'kevin')
  print(b >= c)
  
  
  three_mul = partial(mul, 3)
  print(three_mul(9))
  print(reduce(mul, a))
  
  
  def clock(func):
      @wraps(func)
      def clocked(*args, **kwargs):
          t0 = time.perf_counter()
          res = func(*args, **kwargs)
          t1 = time.perf_counter()
          print('func:{} args:{} cost:{}'.format(func, args, t1 - t0))
          return res
      return clocked
  
  
  @lru_cache()
  @clock
  def fib(n):
      if n < 3:
          return 1
      return fib(n - 1) + fib(n - 2)
  
  
  t0 = time.perf_counter()
  print(fib(30))
  t1 = time.perf_counter()
  print('total:{}'.format(t1 - t0))
  print(fib.__name__)
  print(fib.cache_info())
  
  
  Point = namedtuple('Point', ['x', 'y'])
  p = Point(1, 2)
  print(p)
  
  
  @singledispatch
  def typecheck():
      pass
  
  
  @typecheck.register(int)
  def _(text):
      print(type(text))
      print('---int---')
  
  
  @typecheck.register(str)
  def _(text):
      print(type(text))
      print('---str---')
  
  
  @typecheck.register(float)
  def _(text):
      print(type(text))
      print('---float---')
  
  
  typecheck('ring')