In Python, the term enumeration refers to the process of assigning fixed constant values to a set of strings so that each string can be identified by the value bound to it. The Enum class included in enum module (which is a part of Python’s standard library) is used as the parent class to define enumeration of a set of identifiers − conventionally written in upper case.
In the below code, “subjects” is the enumeration. It has different enumeration members and each member is an object of the enumeration class subjects. These members have name and value attributes.
# importing enum from enum import Enum class subjects(Enum): ENGLISH = 1 MATHS = 2 SCIENCE = 3 SANSKRIT = 4 obj = subjects.MATHS print (type(obj))
Output:
It results in following output −
An enum class cannot have the same member appearing twice, however, more than one member may be assigned the same value. To ensure that each member has a unique value bound to it, use the @unique decorator.
In this example, we are using the @unique decorator to restrict duplicacy.
from enum import Enum, unique @unique class subjects(Enum): ENGLISH = 1 MATHS = 2 GEOGRAPHY = 3 SANSKRIT = 2
Output:
This will raise an exception as shown below −
@unique
^^^^^^
raise ValueError(‘duplicate values found in %r: %s’ %
ValueError: duplicate values found in
The Enum class is a callable class, hence you can use its constructor to create an enumeration. This constructor accepts two arguments, which are the name of enumeration and a string consisting of enumeration member symbolic names separated by a whitespace.
Following is an alternative method of defining an enumeration −
from enum import Enum
subjects = Enum("subjects", "ENGLISH MATHS SCIENCE SANSKRIT")
print(subjects.ENGLISH)
print(subjects.MATHS)
print(subjects.SCIENCE)
print(subjects.SANSKRIT)
Output:
This code will give the following output −
subjects.ENGLISH
subjects.MATHS
subjects.SCIENCE
subjects.SANSKRIT
Members of an enum class can be accessed in two modes −
The following example illustrates how to access value and name of the enum member.
from enum import Enum class subjects(Enum): ENGLISH = "E" MATHS = "M" GEOGRAPHY = "G" SANSKRIT = "S" obj = subjects.SANSKRIT print(type(obj)) print(obj.name) print(obj.value)
Output:
It will produce the following output −
SANSKRIT
S
You can iterate through the enum members in the order of their appearance in the definition, with the help of a for loop.
The following example shows how to iterate through an enumeration using for loop −
from enum import Enum class subjects(Enum): ENGLISH = "E" MATHS = "M" GEOGRAPHY = "G" SANSKRIT = "S" for sub in subjects: print (sub.name, sub.value)
Output:
It will produce the following output −
ENGLISH E
MATHS M
GEOGRAPHY G
SANSKRIT S
We know that enum member can be accessed with the unique value assigned to it, or by its name attribute. Hence, subjects(“E”) as well as subjects[“ENGLISH”] returns subjects.ENGLISH member.
Key Takeaway: Master Python enums—define constants with Enum class—at Vista Academy!