How to create a dictionary in python-Python Tutorial-php.cn

How to create a dictionary in python

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Release： 2019-06-17 13:19:39

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How to create a dictionary in python

python dictionary definition

Dictionary is another mutable container model and can store any type of object.

Each key-value key=>value pair in the dictionary is separated by colon :. Each key-value pair is separated by comma,. The entire dictionary is included in curly braces {}. The format is as follows:

d = {key1 : value1, key2 : value2 }

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The key is generally unique. If the last key-value pair is repeated, the previous one will be replaced. The value does not need to be unique.

>>>dict = {&#39;a&#39;: 1, &#39;b&#39;: 2, &#39;b&#39;: &#39;3&#39;}
>>> dict[&#39;b&#39;]
&#39;3&#39;
>>> dict
{&#39;a&#39;: 1, &#39;b&#39;: &#39;3&#39;}

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Other common ways to create a dictionary in Python:

Dynamic assignment of key values

>>> d ={}
>>> d[&#39;name&#39;] = &#39;Allen&#39;
>>> d
{&#39;name&#39;: &#39;Allen&#39;}

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If needed This method is more appropriate if you dynamically create one field of a dictionary at a time.

Dictionary key-value table

>>> c = dict(name=&#39;Allen&#39;, age=14, gender=&#39;male&#39;)
>>> c
{&#39;gender&#39;: &#39;male&#39;, &#39;age&#39;: 14, &#39;name&#39;: &#39;Allen&#39;}

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Because this form has simple syntax and is less error-prone, it is very popular.

This form requires less code than constants, but the keys must all be strings, so the following code will report an error:

>>> c = dict(name=&#39;Allen&#39;, age=14, gender=&#39;male&#39;, 1=&#39;abcd&#39;)
  File "<stdin>", line 1
SyntaxError: keyword can&#39;t be an expression

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Dictionary key value tuple table

>>> e=dict([(&#39;name&#39;,&#39;Allen&#39;),(&#39;age&#39;,21),(&#39;gender&#39;,&#39;male&#39;)])
>>>
>>>
>>> e
{&#39;gender&#39;: &#39;male&#39;, &#39;age&#39;: 21, &#39;name&#39;: &#39;Allen&#39;}

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This method is useful if you need to gradually build the keys and values into a sequence while the program is running.

The values of all keys are the same or assigned initial values

>>> f=dict.fromkeys([&#39;height&#39;,&#39;weight&#39;],&#39;normal&#39;)>>> f
{&#39;weight&#39;: &#39;normal&#39;, &#39;height&#39;: &#39;normal&#39;}

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