Adding and traversing methods of python dictionary key-value pairs-Python Tutorial-php.cn

Adding and traversing methods of python dictionary key-value pairs

高洛峰

Release： 2017-02-23 11:34:25

Original

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Add key-value pairs

First define an empty dictionary

>>> dic={}

Directly Assign a value to a key that does not exist in the dictionary to add

>>> dic[&#39;name&#39;]=&#39;zhangsan&#39;
>>> dic

{&#39;name&#39;: &#39;zhangsan&#39;}

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This method can also be used if the key or value are both variables

>>> key=&#39;age&#39;
>>> value=30
>>> dic[key]=value
>>> dic

{&#39;age&#39;: 30, &#39;name&#39;: &#39;zhangsan&#39;}

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Here you can see that the data in the dictionary is not arranged in order. If you are interested, you can search for the hash table in the data structure

You can also use the setdefault method of the dictionary

>>> dic.setdefault(&#39;sex&#39;,&#39;male&#39;)
&#39;male&#39;
>>> key=&#39;id&#39;
>>> value=&#39;001&#39;
>>> dic.setdefault(key,value)
&#39;001&#39;
>>> dic
{&#39;id&#39;: &#39;001&#39;, &#39;age&#39;: 30, &#39;name&#39;: &#39;zhangsan&#39;, &#39;sex&#39;: &#39;male&#39;}

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Traverse the dictionary

There are two methods here

Method 1: Get the key first, and then pass dic[key ]Get value

>>> for key in dic:
...   print &#39;key is %s,value is %s&#39;%(key,dic[key])
...
key is id,value is 001
key is age,value is 30
key is name,value is zhangsan
key is sex,value is male

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Method 2: Unpack the tuple list returned by the dictionary items() method in sequence

>>> for key,value in dic.items():
...   print &#39;key is %s,value is %s&#39;%(key,value)
...
key is id,value is 001
key is age,value is 30
key is name,value is zhangsan
key is sex,value is male

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If you are not familiar with list, tuple and sequence unpacking, it is best to Baidu to understand them in depth. You can understand it by combining the arrays, List classes and hash tables you are familiar with in C# or JAVA language

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