Detailed explanation of enumeration types in Python (code examples)

This article brings you a detailed explanation (code example) of enumeration types in Python. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Python’s native types do not include enumeration types. To provide a better solution, Python added the enum standard library in version 3.4 via PEP 435.

The enumeration type can be regarded as a label or a collection of constants, usually used to represent certain limited collections, such as week, month, status, etc. What do we do when there is no specifically provided enumeration type? Generally, it is implemented through a dictionary or class:

Color = {
    'RED'  : 1,
    'GREEN': 2,
    'BLUE' : 3,
}
class Color:
    RED   = 1
    GREEN = 2
    BLUE  = 3

This way of implementing enumeration is of course no problem if it is used carefully. After all, it is a compromise. s solution. The danger is that it can be modified.

Using Enum

A better way is to use the Enum type provided by the standard library. The official library is trustworthy. Versions before 3.4 can also download supported libraries through pip install enum. Simple example:

from enum import Enum
class Color(Enum):
    red = 1
    green = 2
    blue = 3

Enumeration members have values ​​(repeatable by default), and enumeration members have friendly string representations:

>>> print(Color.red)
Color.red
>>> print(repr(Color.red))
<Color.red: 1>
>>> type(Color.red)
<Enum &#39;Color&#39;>
>>> isinstance(Color.green, Color)
True

Enumeration types are not instantiable and cannot be changed.

Define enumeration

When defining an enumeration, the member name is not allowed to be repeated

class Color(Enum):
    red = 1
    green = 2
    red = 3    # TypeError: Attempted to reuse key: 'red'

The member value is allowed to be the same, the second member The name is regarded as an alias of the first member

class Color(Enum):
    red   = 1
    green = 2
    blue  = 1

print(Color.red)              # Color.red
print(Color.blue)             # Color.red
print(Color.red is Color.blue)# True
print(Color(1))               # Color.red  在通过值获取枚举成员时，只能获取到第一个成员

If you cannot define the same member value, you can decorate it with unique

from enum import Enum, unique
@unique
class Color(Enum):
    red   = 1
    green = 2
    blue  = 1  # ValueError: duplicate values found in <enum &#39;Color&#39;>: blue -> red

Enumeration value

You can get members by member name or member value:

print(Color['red'])  # Color.red  通过成员名来获取成员

print(Color(1))      # Color.red  通过成员值来获取成员

Each member has a name attribute and a value attribute:

member = Color.red
print(member.name)   # red
print(member.value)  # 1

supports iteration through members in the defined order. If there are members with duplicate values, only the first duplicate member is obtained:

for color in Color:
    print(color)

Special attributes__members__ is a An ordered dictionary mapping names to members, through which traversal can also be done:

for color in Color.__members__.items():
    print(color)          # ('red', <Color.red: 1>)

Enumeration comparison

Members of an enumeration can be passed through is Identity comparison or equality comparison through ==:

Color.red is Color.red
Color.red is not Color.blue

Color.blue == Color.red
Color.blue != Color.red

Enumeration members cannot perform size comparison:

Color.red < Color.blue    # TypeError: unorderable types: Color() < Color()

Extended enumeration IntEnum

IntEnum is an extension of Enum. Different types of integer enumerations can also be compared with each other:

from enum import IntEnum
class Shape(IntEnum):
    circle = 1
    square = 2

class Request(IntEnum):
    post = 1
    get = 2

print(Shape.circle == 1)            # True
print(Shape.circle < 3)             # True
print(Shape.circle == Request.post) # True
print(Shape.circle >= Request.post) # True

Summary

enum module function is very clear , its usage is also simple, and its implementation method is worth learning. If you have the opportunity, you can take a look at its source code.

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