Python 3 -- 数据结构（list, dict, set,tuple ）

看了《Head First Python》后，觉得写的很不错，适合新手。此处为读书笔记，方便日后查看。

Python 提供了4中数据结构：list,dict,set,tuple. 每种结构都有自己的特征和用处。

1. List -- 有序的可变对象集合

List 的定义

prices = [] # 定义空列表
temps = [32.0, 212.0, 0.0, 81.6, 100.0, 45.3] # 存储浮点型 
words = ['hello','word'] # 存储字符串
car_details = ['Toyota', 'RAV2', 2.2, 60808] # 列表中可以存储混合类型数据
everyting = [prices, temps, words, car_details] # 列表里放置列表

List 常用操作，以下操作直接影响list的值。

fruit=['banana','orange','strawberry']

# 打印列表中全部元素
for v in fruit:
    print(v)

# 判断列表中是否存在某个元素,若不存在加入到列表中。
if 'apple' not in fruit:
    fruit.append('apple')
print(fruit)

# 打印列表长度
print(len(fruit))

# 从列表总添加元素
fruit.append('piers')
print(fruit)

# 从列表中删除某个对象值
numsRem=[1,2,3,4]
numsRem.remove(3)
print('Remove result is '+str(numsRem))
# nums -> [1,2,4]

# 从列表中删除某个位置（索引值）的对象
numsPop=[1,2,3,4]
numsPop.pop() #->4
print('Pop result is '+str(numsPop))
#nums->[1,2,3]

# 加入一个其他列表
nums1=[1,2]
nums2=[3,4]
nums1.extend(nums2)
print(nums1) # [1,2,3,4]

# 从列表的某个位置插入指定元素值
numsIns=[2,3,4]
numsIns.insert(0,1) 
print(numsIns) #[1,2,3,4]

List 和 String 的相互转换

given_message = "It's a known issue."
print("given message original is \'" + given_message +" \'")

# convert string to list
mes_list = list(given_message) 
print("List given message is " + str(mes_list))

# convert list to string
given_message_after = ''.join(mes_list)
print("After converted to string is \'" + given_message_after + " \'")

从list取特定字段，以下操作除了rename以外，其他操作都是生成一个副本，不会改变原list的值。

list1=[1,2,3,4,5,6]
print ("list1 is "+ str(list1))

# It will give a alise for list1, but not copy of it. So if one of them is changed, the other one will be changed also.
list1_rename = list1
print ("list1_rename is " + str(list1_rename))

list1_rename[0]=9
print("After list1_rename[0]=9, list1_rename is " + str(list1_rename))
print("After list1_rename[0]=9, list1 is " + str(list1))

# Copy a list, so if one of it has been changed, the other will not be changed.
list1_copy = list1.copy()
print("list1_copy is " + str(list1_copy))

list1_copy[0]= 8
print("After list1_copy[0]= 8, list1_copy is " + str(list1_copy))
print("After list1_copy[0]= 8, list1 is " + str(list1))

# Get value by index
print("list 1 is " + str(list1))

print("first value is " + str(list1[0])) 
print("last value is " + str(list1[-1])) #navigate index get the value from the end.
print("Value for every 3 index is " + str(list1[0:5:3]))
print("Value from index 3 is " + str(list1[3:]))
print("Value until index 4 is " + str(list1[:4]))
print("value all for every 2 index is " + str(list1[::2]))

# get back ward value
print("Backward value for list1 is " + str(list1[::-1]))
print("Backward value for target range is " + str(list1[4:1:-1]))

2. Dict：

Dict -- 无序的键/值对集合

Dict的定义

dict1 = {}
dict_person = {'Name':'Steven','Gender':'Male','Occupation':'Researcher','Home Planet':'Betelgeuse Seven'} 

print("dict1 is "+ str(dict1))
print("dict_person" + str(dict_person))

Dict的常用操作

dict_person = {'Name':'Steven','Gender':'Male','Occupation':'Researcher','Home Planet':'Betelgeuse Seven'} 

# Get value by index
print("dict_person's name is " + str(dict_person['Name']))

# Add an key and value
dict_person['Age']= 33
print("After dict_person['Age']= 33, dict_person's new:value is " + str(dict_person))

# 遍历dict中的所有key
for k in dict_person:
    print(k)

# 遍历dict中的所有value
for k in dict_person:
    print(dict_person[k])

# 遍历dict中的所有值
for k in dict_person:
    print(k +":" + str(dict_person[k]) + "\t")

# 遍历dict中的所有值
for k,v in dict_person.items():
    print(k +":" + str(dict_person[k]) + "\t")

# 遍历dict中的所有值(按顺序显示)
for k,v in sorted(dict_person.items()):
    print(k +":" + str(dict_person[k]) + "\t")

# 用字典记录频度， 输出给定字符串中元音出现的次数
count_for_string = 'Hello, hello, how are you'
vowels = ['a','e','i','o','u']
found ={}
for k in count_for_string:
    if k in vowels:
        found.setdefault(k,0)
        found[k] +=1

字典的嵌套（也就是表）

from pprint  import pprint 

person={}

person['Mother']={'Name':'Luky','Age':'28','Sex':'Female'}
person['Father']={'Name':'Alex','Age':'31','Sex':'Male'}
person['Son1']={'Name':'Ethan','Age':'3','Sex':'Male'}
person['Son2']={'Name':'Ringo','Age':'1','Sex':'Female'}

# 显示整张嵌套列表
for k,v in sorted(person.items()):
    print(str(k) + ':' + str(v))

for k,v in sorted(person.items()):
    pprint(str(k) + ':' + str(v))

# 显示嵌套列表的某个值
print(person['Mother']['Age'])

3. Set

Set -- 无序的唯一对象集合（不允许有重复，可以用于去重）

Set 的定义：

# 定义空字符串
set_a=()
print(set_a)

# 从列表创建集合
set_volew=set('aaioeuu')
print(set_volew)

Set的常用：

# 并集
volews=set('aeiou')
world="Hello,Apple"
union_letters=volews.union(set(world))
print(union_letters)

# 差集(A-B)，这里是volews letter - world letter
diff_letters=volews.difference(set(world))
print(diff_letters)

# 交集
inst_letters=volews.intersection(set(world))
print(inst_letters)

4. Tuple

Tuple-- 有序的不可变对象集合,其实也是一个一旦创建（并填充数据）就不能改变的列表，这样性能更好。

元组的定义

# 元组的定义
vowels_tuple=('a','e','i','o','u')
print(vowels_tuple)

元组常用操作

# 给元组更新值会报错，因为元组值是不能变的。
# 如vowels_tuple[2]='A' 会报TypeError: 'tuple' object does not support item assignment

# 显示某个元素
print(vowels_tuple[0])

# 只有一个对象的元组赋值一定要加','号，否则不会被视为元组.
tuple=('python')
print(type(tuple)) # <class 'str'>

tuple2=('python',)
print(type(tuple2)) # <class 'tuple'>

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Python 3 -- 数据结构（list, dict, set,tuple ）

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