[07] python learning system to read a map and learn how to operate dictionary

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Data Types - Dictionary (dict)

table of Contents:

• Get a picture dictionary
• What is the dictionary
  • js object
• Dictionary long-sawed
  • Pseudo-code syntax
  • Examples demo
  • Syntax imaging
• How to use the dictionary
  • Get the length of the dictionary function --len
  • Extraction dictionary elements
  • Nested extract
  • Add elements to the dictionary
  • Delete dictionary elements
• Comparison of set list
  • Same point
  • difference
• Exercises

Get a picture dictionary

A little knowledge points get a picture dictionary

If the knowledge described in the figure too general, see the following fine text:

What is the dictionary

js object

When it comes to the dictionary, front-end students can understand it as: object. Because the object of long python and js in the dictionary can not say like, it is simply the same.

Dictionary is a collection of key-value pairs to more than one to one child elements.

It is the same list, just as a data type of complex.

Wherein the key name in the dictionary must be a string type, and the value corresponding to the keys may be of any type.

Dictionary long-sawed

Having said that, the dictionary in the end sawed? Unveiled:

Pseudo-code syntax

列表变量名 = {
  '字符串键名key1': 对应key1的值value1, 
  '字符串键名key2': 对应key2的值value2, 
  ...(更多key、value对儿)
}

Examples demo

A dictionary definition of the demo code, you can pay attention to the next, the next case might be used.

dictName = {
  'name': '小石头',
  'age': 19,
  'hobby': {
    'it': ['css','js','python'],
    'daily': [['music','tv'],['apple','pear']],
    'sports': 'sleep'
  },
  'married': True
}

Syntax imaging

By pseudo-code and demo code that we can conclude the following characteristic points on the dictionary:

• Custom variable names

• The dictionary assigned to the variable equal sign (dictName)

• The right of the equal sign is a dictionary, with a child wrapped in one pair of braces

• Internal dictionary is a pair of key-value pair (key: key; Found: value).

• 键名 scripts welfare

  • That is the key name must be wrapped in quotes, otherwise it will error
  • Error type: NameError variable undefined error

• Key names are not the only need to repeat

  • Above, dictName, the only one "age"
  • If there are multiple keys with the same name, leaving only the last key

  keyNameOnly = {
    'age': 29,
    'age': 19,
    'name': '小石头'
  }
  print(keyNameOnly) 
  # {'age': 19, 'name': '小石头'} age对应29的键值对被覆盖了
  

• Value can be any type of value

• A target value of the content may be repeated

    valueNameRepeat = {
      'name': '小石头',
      'like': '小石头',
      'realTalk': True
    }
    print(valueNameRepeat)
    # {'name': '小石头', 'like': '小石头', 'realTalk': True} 值‘小石头’重复也无所谓。
  

• Colon connection between the key identifier and the value

• Key (key) combined value (value) is formed with a pair of keys, called child

• Each pair of children between the keys on separated by commas

• Dictionary can have any number of key-value pairs children

• The last key-value pairs of children do not need a comma

How to use the dictionary

Get the length of the dictionary function --len

我们可以用len()函数来得出一个列表或者字典的长度（元素个数）

括号里放列表或字典名称

print(len(dictName))  #4，因为又4对儿，键名分别是name、age、hobby和married

列表的长度也是用len()函数获取

提取字典中的元素

通过字典的索引(键名)来获取对应的值

伪代码:

字典名[字典的键]

字典没有偏移量，所以中括号写的是键名

demo:

dictName['name'] # 小石头

嵌套提取

拓展 - 二维嵌套列表值的提取方法

同样是用偏移量来获取。

listdemo = [['music','tv'],['apple','pear']]
print(listdemo[1][1]) # pear

先用第一个偏移量获取最外边列表的第1个元素。得到列表['apple','pear']后，再继续追加一个偏移量[1]获取得到的列表['apple','pear']中第一个元素，打印出'pear'

拓展 - 多维嵌套字典中值的提取方法

因为是用键名，而不是偏移量的方法获取。所以感觉在理解逻辑上，比列表容易让初学者接受。

print(dictName['hobby']['sports']) # sleep

先用键名"hobby"获取其对应的值，再用“hobby”里的"sports"获取其sports自己对应的值。得到"sleep"

拓展 - 列表与字典互相嵌套时值的提取方法

举一反三，概念加强版

print(dictName['hobby']['daily'][0][0]) # music

往字典中增加元素

新增键值对要用到赋值语句 伪代码：

字典名[键] = 值

自我感觉很好理解。只需要在提取的基础上赋值即可。

⚠️但可能需要注意，如果键名是字典中已经存在的，再这么操作就会直接修改这个键的值。

示例代码：

dictName['homeland'] = 'china'
print(dictName)

删除字典中的元素

删除字典里键值对的代码是del语句

伪代码：

del 字典名[键]

示例代码：

del(dictName['married'])
print(dictName)

对比列表的异同

相同点

1、修改值时都是通过赋值：在列表和字典中，如果要修改元素，都可用赋值语句来完成

2、值类型支持任意嵌套：除基本数据类型外，列表可嵌套其他列表和字典，字典也可嵌套其他字典和列表。

不同点

1、比较相等时规则不同

列表中的元素是有自己明确的“位置”的，所以即使看似相同的元素，只要在列表所处的位置不同，它们就是两个不同的列表

而字典中的数据是随机排列的，所以相比时即使键调动顺序也不影响

代码观察：

students1 = ['小明','小红','小刚']
students2 = ['小明','小红','小刚']
print(students1 == students2) 
# True 必须元素顺序、个数、内容皆一致则相同

students3 = ['小明','小红','小刚']
students4 = ['小明','小刚','小红']
print(students3 == students4) 
# False 改变了一下顺序就不相等了


scores1 = {'小明':95,'小红':90,'小刚':100}
scores2 = {'小刚':100,'小明':95,'小红':90}
print(scores1 == scores2) 
# True 只要两个字典中，键名及其分别对应的值都一一相等，则整个字典相等。

scores3 = {'小明':95,'小红':90,'小刚':100}
scores4 = {'小明':9,'小红':90,'小刚':100}
print(scores3 == scores4) 
# False 这样，即使键名一一对应，键名所对应的值不同，最终结果不相等。

2、读取数据的方法不同

列表有序，要用偏移量定位

字典无序，可通过唯一的键来取值

观察代码：

# 提取列表中的数据 - 用偏移量/索引/下标
listdemo = ['apple','pear']
print(listdemo[1]) # pear

# 提取字典中的数据 - 用键名
keyNameOnly = {
  'age': 29,
  'age': 19,
  'name': '小石头'
}
print(keyNameOnly['age']) # 19

练习题

you = {
  'name': '',
  'a': [{
    'b': {
      'c': '强撑',
      'love': 'anybody'
    }
  }],
  'age': 30
}

4、在b里边增加爱好，为一个数组，数组内容自定
3、删除“age”
2、修改“name”的值
1、提取出“love”的值