Python--迭代

字典迭代

names = {'Mary Wang': 'She is very cute',
         'William Liu': 'He is very handsome',
         'Tom Zhao': 'He is a little bit shy',
         'Jary Qian': 'He is very rich'}
for key, value in names.items():
    print('Name:{}     Saying:{}'.format(key, value))

Name:Mary Wang     Saying:She is very cute
Name:William Liu     Saying:He is very handsome
Name:Tom Zhao     Saying:He is a little bit shy
Name:Jary Qian     Saying:He is very rich

Zip迭代

• zip

  names = ['William', 'Mary', 'Tommy', 'Jimmy']
  heights = [185, 175, 173, 164]
  print(list(zip(names, heights)))
  for i, name in zip(range(len(names)), names):
    print(i+1, name)

• William
• Mary
• Tommy

• Jimmy

• zip迭代器和Enumerate()

  names = ['William', 'Mary', 'Tommy', 'Jimmy']
  for i, name in enumerate(names):
    print(i+1,name)

• William
• Mary
• Tommy

• Jimmy

  ---

• zip迭代器zip()反向

  • zip(*)--进行反向

  names = ['William', 'Mary', 'Tommy', 'Jimmy']
  heights = [185, 175, 173, 164]
  names_heights = list(zip(names, heights))
  print(names_heights)
  names_2, heights_2 = zip(*names_heights)
  print(names_2)

  [('William', 185), ('Mary', 175), ('Tommy', 173), ('Jimmy', 164)]
  ('William', 'Mary', 'Tommy', 'Jimmy')

  ---

迭代器和生成器

• 迭代器:iterator

  • 列表是可以迭代的对象但不是迭代器
  • 迭代器是一个数据流,没有生成出来
  • enumerate就是1个迭代器

  list_1 = [1,2,3,4,5,6,7,8,9]
  print(enumerate(list_1))

  <enumerate object at 0x00000245FC4425A0>

  ---

  list_1 = [1,2,3,4,5,6,7,8,9]
  print(list(enumerate(list_1)))

  [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 6), (6, 7), (7, 8), (8, 9)]

  开始序号可以更改

• 生成器:generator

  • 用函数可以创造迭代器(利用yield一次返回一个值)

  def my_range(x):
    a=0
    while a<x:
        yield a
        a+=1
  print(my_range(20))
  print(list(my_range(20)))

  <generator object my_range at 0x000001DE950227C8>
  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

  ---

• 自己创建的迭代器

  • 迭代器可以少占用内存
  • 如果list内容过多,内存存储不下需要使用迭代器

• 自己编写enumerate()

  steps=['Python','Git','Deap','AI']
  def my_enumerate(iterable, star = 0):
    count=star
    for element in iterable:
       yield count,element
        count+=1
  for i,step in my_enumerate(steps,1):
    print('Step{}:{}'.format(i,step))

  Step1:Python
  Step2:Git
  Step3:Deap
  Step4:AI

• 编写生成器对大数据进行拆分

  def chunker(iterable,size):
    for i in range(0,len(iterable),size):
        yield iterable[i:i+size]
  
  for chunk in chunker(range(100),20):
    print(list(chunk))

  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
  [20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39]
  [40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59]
  [60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79]
  [80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]