#27777: File object does not consistently open itself in context manager use
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Reporter: Raphael Gaschignard | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.10
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Django's {{{File}}} object has an open method that will reseek the file to
0, and re-open the file if necessary (after closure).
Unfortunately, the context manager does not automatically open a file. In
particular, {{{FieldFile}}} relies on implicit opening via the file
property to open a file, but caches the object internally. Since the
context manager for {{{File}}} closes the file after use, this means that
using the context manager twice in a row fails (since the file is not re-
opened).
{{{
class C(Model):
pdf = FileField(...)
c = C.objects.get()
with c.pdf as pdf: # file not opened yet
print(c.size) # pdf.size accesses pdf.file, which will implicitly
open the file
# file is closed at the end of a context manager
with c.pdf as pdf:
print(c.size) # pdf.size now uses cached file, which is already
closed!
}}}
I think it makes sense to have the context manager({{{__enter__}}}) call
{{{open}}} on the object, so that files can be used in multiple context
managers without having to to an open-ness check.
our current workaround is to check for closed-ness on all context manager
uses:
{{{
with c.pdf as pdf:
if pdf.closed():
pdf.open() # seeks the file to 0 and opens if necessary
# do "real" work
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/27777>
Django <https://code.djangoproject.com/>
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