详解python内置常用高阶函数(列出了5个常用的)

def add(x):
 return x+x
print(map(add,[1, 2, 3]))
# Out:<map object at 0x00000239E833DE48>
print(list(map(add,[1, 2, 3])))
# Out:[2, 4, 6]

from functools import reduce
def prod(x, y):
 return x*y
print(reduce(prod, [2, 4, 5, 7, 12]))
# Out:3360 # 2*4*5*7*12
# reduce()还可以接收第3个可选参数，作为计算的初始值。如果把初始值设为100
print(reduce(prod, [2, 4, 5, 7, 12], 100))
# Out:336000 # 2*4*5*7*12*100

import math
def is_sqr(x):
 return math.sqrt(x) == int(math.sqrt(x))
print(list(filter(is_sqr, range(1, 101))))
# Out:[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

print(sorted([5, 2, 3, 1, 4]))
# Out:[1, 2, 3, 4, 5]
print(sorted({1:'D', 2:'B', 3:'B', 4:'E', 5: 'A'}))
# Out:[1, 2, 3, 4, 5]

example_list = [5, 0, 6, 1, 2, 7, 3, 4]
result_list = sorted(example_list, key=lambda x: x*-1)
print(result_list)

example_list = [5, 0, 6, 1, 2, 7, 3, 4]
print(sorted(example_list, reverse=True))
# Out:[7, 6, 5, 4, 3, 2, 1, 0]

def my_abs():
 return abs # 返回函数，返回函数可以把一些计算延迟
def my_abs2(x):
 return abs(x) # 返回函数调用的结果，返回值是一个数值

def calc_prod(lst):
 def lazy_prod():
  prod = 1
  for i in lst:
   prod = prod*i
  return prod
 return lazy_prod
f = calc_prod([1, 2, 3, 4])
print(f())
# Out:24

def f():
 print('call f()...')
 # 定义函数g:
 def g():
  print('call g()...')
 # 返回函数g:
 return g

def calc_sum(lst):
 return sum(lst)
print(calc_sum([1,2,3,4]))
# Out:10

def calc_sum(lst):
 def lazy_sum():
  return sum(lst)
 return lazy_sum

f = calc_sum([1, 2, 3, 4])
print(f) # 代码并没有对函数进行执行计算出结果，而是返回函数,所以打印出来的是类型
#Out: <function calc_sum.<locals>.lazy_sum at 0x000001FF43462E18>
print(f())  # 对返回的函数进行调用时，才计算出结果
# Out:10