Python Enumerate in Django Choice Field

Enumerate() in Python

The enumerate() method adds counter to an iterable and returns it (the enumerate object).

enumerate() Parameters

enumerate() method takes two parameters:

• iterable - a sequence, an iterator, or objects that supports iteration
• start (optional) - enumerate() starts counting from this number. If start is omitted, 0 is taken as start.

Now let's how we could use Enumerate in Django Framework.

Below Django example only < Django 3.0 version. In Django 3.0 there is TextChoiceField introduced, where we could use the enum directly.

Django Enumerate ChoiceField

Example:

APPROVE_CHOICE = ['APPROVED','PENDING']

enumerateChoice = enumerate(APPROVE_CHOICE)

print(type(enumerateChoice))

# converting to list
print(list(enumerateChoice))

# changing the default counter
enumerateChoice = enumerate(APPROVE_CHOICE , 5)
print(list(enumerateChoice))

Output 

<class 'enumerate'>
[(0, 'APPROVED'), (1, 'PENDING')]
[(5, 'APPROVED'), (6, 'PENDING')]

In this post, I will walk you through using Enum as choices of field with a simple example. Assume there is a Post model where we need to enable the APPROVED/PENDING choice type in our choice Field.

First, we define a class for all choices:

class Post(models.Model):
    title = models.CharField(max_length=60)
    status = models.CharField(
        blank=True, choices=[(stat, stat.value) for stat in StatusType], max_length=20)

Using Enum

Now we have defined our Enums and model, how would we use it?

class StatusType(Enum):
    APPROVED = "APPROVED"
    PENDING = "PENDING"

Below are the way to create the enum related field 

>>> from blog.models import Post
>>> from enum import Enum
>>> class StatusType(Enum):
...     APPROVED = "APPROVED"
...     PENDING = "PENDING"
...
>>> p = Post(title='hi',status=StatusType.PENDING)
>>> p.save()

Note that how we supply the value for parameter status depends on the first element we defined in the Tuples of the list of choices. We use (stat, stat.value) which stat being an Enum type.

Below details, I have grabbed from some of the various article,

Why Enum?

You may ask, “Why using Enum instead of the examples given in Django official documentation?”

• To distinct from any other values within sets of values. For example, we could simple define integer 1–7 for days in a week, what about we have another set of values its representation includes the subset of 1–7?
• Central Repository of predefined values, Enumeration can be used across your entire program, not just your in your models.

When to use Enum?

According to PEP 435, an enumeration are useful for defining an immutable, related set of constant values that may or may not have a semantic meaning. Classic examples are days of the week (Sunday through Saturday) and school assessment grades (‘A’ through ‘D’, and ‘F’). Other examples include error status values and states within a defined process.