Python 列表、字典的几种遍历方式

列表遍历使用高阶函数代码看起来更加简洁明了，普通for in遍历更加灵活。

字典可以很容易的通过函数获取keys和values列表，for in也有几种不同的方式。

from functools import reduce


def foo0():
  print('高阶函数遍历')
  # 将列表中的元素翻倍
  ls = [1, 2, 3, 4, 5, 6]
  ls2 = list(map(lambda x: x * 2, ls))
  print(ls2)

  # 过滤保留偶数
  ls3 = list(filter(lambda x : x % 2 == 0, ls))
  print(ls3)

  # 列表元素和
  sum = reduce(lambda x,y: x+y, ls)
  print(sum)


def foo1():
  print('普通for in遍历')
  ls = [1, 2, 3, 4, 5, 6]
  ls2 = []
  for v in ls:
    ls2.append(v * 2)
  print(ls2)

  ls3 = []
  for v in ls:
    if v % 2 == 0:
      ls3.append(v)
  print(ls3)

  sum = 0
  for v in ls:
    sum += v
  print(sum)


def foo2():
  print('带下标的for循环')
  ls = [1, 2, 3, 4, 5, 6]
  for i, v in enumerate(ls):
    ls[i] = v * 2
  print(ls)

  for i in range(len(ls)):
    ls[i] *= 2
  print(ls)


def foo3():
  print('字典的几种遍历方式')
  d = {'color': 'red', 'fruit': 'apple', 'pet': 'dog'}

  print('输出keys列表', d.keys())
  print('输出所有values列表', d.values())
  
  print('输出所有key:')
  for key in d:
    print(key)

  print('输出key和value:')
  for key in d:
    print(key, '->', d[key])

  print('输出列表，元素是tuple:')
  for item in d.items():
    print(item[0], ',', item[1])

  print('输出key和value:')
  for k, v in d.items():
    print(k, v)
  

if __name__ == "__main__":
  foo0()
  foo1()
  foo2()
  foo3()