Take stock of the basics of Python dictionaries

Release: 2023-07-25 16:19:51
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1. Foreword

If there is a list and the name "xiaoWang" needs to be modified, the code must be modified through the corresponding index value.

  nameList = ['xiaoZhang', 'xiaoWang', 'xiaoLi']
  nameList[1] = 'xiaoxiaoWang
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If the order of the list has changed, as follows:

  nameList = ['xiaoWang', 'xiaoZhang',  'xiaoLi'];
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At this time, you need to modify the subscript to complete the name Modifications.

  nameList[0] = 'xiaoxiaoWang'
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Is there a way to store multiple data and locate the required element easily while accessing the element? This is the dictionary.


2. Introduction to dictionaries

  • Dictionaries and lists Similarly, multiple data can also be stored.

  • #When looking for an element in the list, it is based on the subscript.

  • When looking for an element in the dictionary, it is based on the 'name' (that is, the value in front of the colon:, such as 'name', ' id', 'sex').

  • #Each element of the dictionary consists of 2 parts, key: value. For example, 'name':'monitor', where 'name' is the key and 'monitor' is the value.

  • Access value based on key

    Example:

# #
  info = {'name':'班长', 'id':100, 'sex':'f', 'address':'地球亚洲中国北京'}
    print(info['name'])        print(info['address'])
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Run result:

Take stock of the basics of Python dictionaries

若访问不存在的键,则会报错:

>>> info['age']
Traceback (most recent call last):  File "<stdin>", line 1, in <module>  KeyError: &#39;age&#39;
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在我们不确定字典中是否存在某个键而又想获取其值时,可以使用get方法,还可以设置默认值。

>>> age = info.get(&#39;age&#39;)>>> age    #&#39;age&#39;键不存在,所以age为None>>> type(age)<type &#39;NoneType&#39;>>>> age = info.get(&#39;age&#39;, 18) # 若info中不存在&#39;age&#39;这个键,就返回默认值18>>> print(age) 18  #运行结果
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1. 字典的常见操作1

<1> 添加元素

   info = {&#39;name&#39;:&#39;班长&#39;, &#39;sex&#39;:&#39;f&#39;, &#39;address&#39;:&#39;地球亚洲中国北京&#39;}
    print(&#39;id为:%d&#39;%info[&#39;id&#39;])
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运行结果:

Take stock of the basics of Python dictionaries

如果在使用 变量名['键'] = 数据 时,这个“键”在字典中,不存在,那么就会新增这个元素。

添加新的元素。

   info = {&#39;name&#39;:&#39;班长&#39;, &#39;sex&#39;:&#39;f&#39;, &#39;address&#39;:&#39;地球亚洲中国北京&#39;}
    # print(&#39;id为:%d&#39;%info[&#39;id&#39;])#程序会终端运行,因为访问了不存在的键
    newId = input(&#39;请输入新的学号&#39;)
    info[&#39;id&#39;] = newId
    print(&#39;添加之后的id为:%d&#39;%info[&#39;id&#39;])
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运行结果:

   请输入新的学号188   添加之后的id为: 188
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<2> 删除元素

对字典进行删除操作,有一下几种:

  • del

  • clear()

del删除指定的元素

   info = {&#39;name&#39;:&#39;班长&#39;, &#39;sex&#39;:&#39;f&#39;, &#39;address&#39;:&#39;地球亚洲中国北京&#39;}
    print(&#39;删除前,%s&#39;%info[&#39;name&#39;])
    del info[&#39;name&#39;]
    print(&#39;删除后,%s&#39;%info[&#39;name&#39;])
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运行结果:

Take stock of the basics of Python dictionaries

del删除整个字典。

   info = {&#39;name&#39;:&#39;monitor&#39;, &#39;sex&#39;:&#39;f&#39;, &#39;address&#39;:&#39;China&#39;}
    print(&#39;删除前,%s&#39;%info)
    del info
    print(&#39;删除后,%s&#39;%info)
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运行结果:

Take stock of the basics of Python dictionaries

clear清空整个字典。

   info = {&#39;name&#39;:&#39;monitor&#39;, &#39;sex&#39;:&#39;f&#39;, &#39;address&#39;:&#39;China&#39;}
    print(&#39;清空前,%s&#39;%info)
    info.clear()
    print(&#39;清空后,%s&#39;%info)
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运行结果:

Take stock of the basics of Python dictionaries

<3> 修改元素

字典的每个元素中的数据是可以修改的,只要通过key找到,即可修改。

   info = {&#39;name&#39;:&#39;班长&#39;, &#39;id&#39;:100, &#39;sex&#39;:&#39;f&#39;, &#39;address&#39;:&#39;地球亚洲中国北京&#39;}
    newId = input(&#39;请输入新的学号&#39;)
    info[&#39;id&#39;] = int(newId)
    print(&#39;修改之后的id为%d:&#39;%info[&#39;id&#39;])
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运行结果:

Take stock of the basics of Python dictionaries


2. 字典的常见操作2

<1>len()

测量字典中,键值对的个数。

dict={"name":&#39;zahnsan&#39;,&#39;sex&#39;:&#39;m&#39;}
print(len(dict))
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运行结果:

Take stock of the basics of Python dictionaries

<2>keys

返回一个包含字典所有KEY的列表。

dict={"name":&#39;zahnsan&#39;,&#39;sex&#39;:&#39;m&#39;}
print(dict.keys())
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运行结果:

Take stock of the basics of Python dictionaries

<3>values

返回一个包含字典所有value的列表。

dict={"name":&#39;zahnsan&#39;,&#39;sex&#39;:&#39;m&#39;}
print(dict.values())
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运行结果:

Take stock of the basics of Python dictionaries

<4>items

返回一个包含所有(键,值)元祖的列表。

dict={"name":&#39;zahnsan&#39;,&#39;sex&#39;:&#39;m&#39;}
print(dict.items())
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运行结果:

Take stock of the basics of Python dictionaries


三、遍历

语法:通过for ... in ...:的语法结构,我们可以遍历字符串、列表、元组、字典等数据结构。

注意 :Python语法的缩进

先看一下字符串,列表和元组是怎么遍历的。

字符串遍历

>>> a_str = "hello itcast">>> for char in a_str:...     print(char,end=&#39; &#39;)...h e l l o   i t c a s t #运行结果
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列表遍历

>>> a_list = [1, 2, 3, 4, 5]>>> for num in a_list:...     print(num,end=&#39; &#39;)...1 2 3 4 5 #运行结果
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元组遍历

>>> a_turple = (1, 2, 3, 4, 5)>>> for num in a_turple:...     print(num,end=" ")1 2 3 4 5 #运行结果
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字典遍历

1 . 遍历字典的key(键)

Take stock of the basics of Python dictionaries

2 . 遍历字典的value(值)

Take stock of the basics of Python dictionaries

3. 遍历字典的项(元素)

Take stock of the basics of Python dictionaries

4. 遍历字典的key-value(键值对)

Take stock of the basics of Python dictionaries


5. enumerate()

chars = [&#39;a&#39;, &#39;b&#39;, &#39;c&#39;, &#39;d&#39;]for i, chr in enumerate(chars):    print(i, chr)
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运行结果:

Take stock of the basics of Python dictionaries


四、总结

本文以生活中字典的实际应用,主要介绍了Python字典的基础知识,用丰富的案例,帮助大家更好的去了解字典常见的的基础操作。

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