浅谈python之高阶函数和匿名函数

def func(x):
 return x*x

r = map(func, [1, 2, 3, 4, 5])
print(type(r))
r = list(r)
print(r)

from functools import reduce

def fn(x, y):
 return x * 10 + y

f = reduce(fn, [1, 3, 5, 7, 9]) # 把序列变为整数
print(f)
print(type(f))

from functools import reduce

def fn(x, y):
 return x * 10 + y

def char2num(s):
 digits = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}
 return digits[s]

f = reduce(fn, map(char2num, '13579'))
print(f)

def not_empty(s):
  return s and s.strip()　　# 不能直接写s.strip()
 
 f = filter(not_empty, ['A', '', 'B', None, 'C', ' '])
 print(type(f))
 print(list(f))

l = sorted([36, 5, -12, 9, -21], key=abs) # 按绝对值大小排序
print(l)

s = sorted(['bob', 'about', 'Zoo', 'Credit'])  # 按ASCII大小排序
print(s)

sl = sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower) # 忽略大小写排序
print(sl)

sr = sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower, reverse=True)  # 反向排序
print(sr)

from operator import itemgetter　　　　# 需要使用operator模块
L = [('Bob', 75), ('Adam', 92), ('Bart', 66), ('Lisa', 88)]
print(sorted(L, key=itemgetter(0)))

from operator import itemgetter

dic = {"Bob": 75, "Adam": 92, "Lisa": 88}

print(sorted(dic,key=itemgetter(0)))

print(sorted(dic, key=itemgetter(1)))

f = list(map(lambda x: x * x, [1, 2, 3, 4, 5, 6, 7, 8, 9]))
print(f)

 def f(x):
 return x * x