#23222: Empty BinaryField != b'' on Python 2
-------------------------------------+-------------------------------------
Reporter: wkschwartz@… | Owner: gregorth
Type: Bug | Status: assigned
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by wkschwartz:
Old description:
> = Problem =
>
> 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!
>
> See http://stackoverflow.com/q/12625557/1286628
>
> 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)
>
> 1. Make a new project and a new app and add the app to settings.py
> 2. Fill in `app/models.py` as follows
>
> {{{#!python
> from django.db import models
> class BinModel(models.Model):
> data = models.BinaryField()
> }}}
>
> 3. Run from the command line:
>
> {{{#!bash
> (venv) $ ./manage.py makemigrations app ./manage.py migrate &&
> ./manage.py shell
> }}}
>
> 4. Run from the resulting Python shell
>
> {{{#!python
> >>> 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.
New description:
= Problem =
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!
See http://stackoverflow.com/q/12625557/1286628
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)
1. Make a new project and a new app and add the app to settings.py
2. Fill in `app/models.py` as follows
{{{#!python
from django.db import models
class BinModel(models.Model):
data = models.BinaryField()
}}}
3. Run from the command line:
{{{#!bash
(venv) $ ./manage.py makemigrations app && ./manage.py migrate &&
./manage.py shell
}}}
4. Run from the resulting Python shell
{{{#!python
>>> 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.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/23222#comment:7>
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