Consider these two styles of code that accomplish the same thing:
Nested imports
common.models
from django.db.models import *
class SmallAutoField(fields.AutoField):
def db_type(self, connection):
return "smallserial"
myapp.models:
from common import models
class Test(models.Model):
id = models.SmallAutoField()
test = models.IntegerField()
Separate imports
common.models
from django.db import models
class SmallAutoField(models.fields.AutoField):
def db_type(self, connection):
return "smallserial"
myapp.models:
from django.db import models
from common import models as my_models
class Test(models.Model):
id = my_models.SmallAutoField()
test = models.IntegerField()
I know which version I prefer stylistically, but which version is the proper way to do it and why?
As for performance: I tried to timeit the Nested version, but that’s not possible because SyntaxError: import * only allowed at module level. So, is there another way to benchmark this method?
Bytecode for reference, but doesn’t look like it tells much:
>>> dis.dis('from django.db.models import *')
1 0 LOAD_CONST 0 (0)
3 LOAD_CONST 1 (('*',))
6 IMPORT_NAME 0 (django.db.models)
9 IMPORT_STAR
10 LOAD_CONST 2 (None)
13 RETURN_VALUE
>>> dis.dis('from django.db import models')
1 0 LOAD_CONST 0 (0)
3 LOAD_CONST 1 (('models',))
6 IMPORT_NAME 0 (django.db)
9 IMPORT_FROM 1 (models)
12 STORE_NAME 1 (models)
15 POP_TOP
16 LOAD_CONST 2 (None)
19 RETURN_VALUE
5
The class SmallAutoField is actually an innovation created for this particular application – it’s an improvement. It “moves the ball down the field” so to speak, upgrading the ability to describe persistence.
For a new reader of the program years from now (e.g. an engineer who needs to understand what it does) the intent of the second style is slightly clearer overall: they can easily see that “models” refers to to Django.db.models and “my_models” to something new.
The second style, highlights the credit awarded for the innovation by calling it “my_models.” It might be good to highlight the intent further like “serial_id_models” or “advanced_models.”
HTH — Rich