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This article mainly explains "how to define and use Python enumeration class". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to define and use Python enumerated classes.

For some classes with special meaning, in fact, the number of instantiated objects is often fixed. For example, if you use one class to represent the month, the maximum number of instance objects of this class is 12; for example, if you use one class to represent the season, the maximum number of instantiated objects of this class is 4.

For this special class, a new Enum enumeration class has been added to Python 3.4.The Enum enumeration class has been added to this special class. That is, these classes with a fixed number of instantiated objects can be defined by enumerated classes.

For example, the following program demonstrates how to define an enumeration class:

From enum import Enumclass Color (Enum): # specify the value value for the sequence value red = 1green = 2blue = 3

If you want to define a class as an enumerated class, you just need to make it inherit from the Enum class in the enum module. For example, in the above program, the Color class inherits from the Enum class, which proves to be an enumerated class.

In the Color enumeration class, red, green, and blue are all members of the class (which can be understood as class variables). Notice that each member of the enumeration class consists of two parts, name and value, where the name attribute value is the variable name of the enumerated value (such as red), and value represents the ordinal of the enumerated value (the ordinal usually starts with 1).

Unlike normal classes, enumerated classes cannot be used to instantiate objects, but this does not prevent us from accessing members of enumerated classes. There are many ways to access enumerated class members, for example, take the Color enumerated class as an example

Add the following code to it:

# three ways to call enumerated members print (Color.red) print (Color ['red']) print (Color (1)) # call value and nameprint (Color.red.value) print (Color.red.name) in enumerated members # two ways for color in Color:print (color) to traverse all members of enumerated classes

The output of the program is as follows:

Color.red

Color.red

Color.red

one

Red

Color.red

Color.green

Color.blue

Enumeration class members cannot be compared, but can be compared with = = or is for equality, for example

Print (Color.red = = Color.green) print (Color.red.name is Color.green.name)

The output is as follows:

Flase

Flase

It is important to note that enumerating the values of individual members of a class cannot make any changes outside the class, that is, the following syntax is wrong:

Color.red = 4

In addition, the enumerated class provides a _ _ members__ attribute, which is a dictionary containing all the members of the enumerated class, and you can also access individual members of the enumerated class by traversing this property.

For example:

For name,member in Color.__members__.items (): print (name,-> ", member)

The output is as follows:

Red-> Color.red

Green-> Color.green

Blue-> Color.blue

It is worth mentioning that each member of the Python enumeration class must ensure that the name is different from each other, but the value can be the same.

For example:

From enum import Enumclass Color (Enum): # specify the value value for the sequence value red = 1green = 1blue = 3print (Color ['green'])

The output is as follows:

Color.red

As you can see, red and green in the Color enumeration class have the same value (both 1), and Python allows this to happen, and it treats green as an alias for red, so when accessing the green member, the final output is red.

In the actual programming process, if you want to avoid this situation, you can use the @ unique decorator so that when a member of the enumeration class with the same value appears, the program reports a ValueError error.

For example:

# introduce uniquefrom enum import Enum,unique# to add unique decorator @ uniqueclass Color (Enum): # specify value values for sequence values red = 1green = 1blue = 3print (Color ['green'])

Running the program will report an error:

Traceback (most recent call last):

File "D:\ python3.6\ demo.py", line 3, in

Class Color (Enum):

File "D:\ python3.6\ lib\ enum.py", line 834, in unique

(enumeration, alias_details))

ValueError: duplicate values found in: green-> red

In addition to creating an enumerated class by inheriting the methods of the Enum class, you can also create an enumerated class using the Enum () function.

For example:

From enum import Enum# creates an enumerated class Color = Enum ("Color", ('red','green','blue')) # 3 ways to invoke enumerated members print (Color.red) print (Color [' red']) print (Color (1)) # fetches value and nameprint (Color.red.value) print (Color.red.name) # 2 ways for color in Color:print (color) traverses all members of enumerated classes

The Enum () function takes two arguments, the first to specify the class name of the enumerated class, and the second parameter to specify multiple members of the enumerated class.

As shown above, a single line of code creates an enumerated class that is the same as the previous Color class.

Run the program, and the output is as follows:

Color.red

Color.red

Color.red

one

Red

Color.red

Color.green

Color.blue

At this point, I believe you have a deeper understanding of "how to define and use Python enumerated classes". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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