Empty BinaryField != b'' on Python 2
|Reported by:||wkschwartz@…||Owned by:||nobody|
|Component:||Database layer (models, ORM)||Version:||master|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
In Python 2, at least under SQLite, the initial value for an empty binary field behaves inconsistently. The ORM thinks it's an empty bytes: b''. The database connection manager thinks it's a buffer. Now, the buffer evaluates to False and has zero length. So it'll mostly work. But not always -- and most importantly to me, not in my unit tests!
Note this was not a problem under Python 3.4.
Steps to Reproduce
Using Python 2.7.8, SQLite, and either Django 1.7rc2 or Django @ edcc75e5ac5b9dc2f174580e7adacd3be586f8bd (HEAD at the time of this writing; the error exists in both places)
- Make a new project and a new app and add the app to settings.py
- Fill in app/models.py as follows
from django.db import models class BinModel(models.Model): data = models.BinaryField()
- Run from the command line:
(venv) $ ./manage.py makemigrations app ./manage.py migrate && ./manage.py shell
- Run from the resulting Python shell
>>> from app import models; m = models.BinModel(); m.save(); n = models.BinModel.objects.get() >>> m.data '' >>> m.data == b'' True >>> n.data <read-write buffer ptr 0x10eaa62b0, size 0 at 0x10eaa6270> >>> n.data == b'' False >>> bool(n.data) False >>> len(n.data) 0 >>> bytes(n.data) ''
Note that the same problem persisted when I had a default value for the field. There was no problem under Python 3.4.
Change History (5)
comment:1 Changed 7 months ago by CollinAnderson
- Cc cmawebsite@… added
- Needs documentation unset
- Needs tests unset
- Patch needs improvement unset
- Severity changed from Release blocker to Normal
- Version changed from 1.7-rc-2 to master
comment:3 Changed 7 months ago by CollinAnderson
- Summary changed from Empty BinaryField != b'' in Python 2/SQLite to Empty BinaryField != b'' on Python 2