#26040 (Streaming Large CSV Files Example Incorrect) – Django (original) (raw)
#26040 closed Bug (invalid)
| Reported by: | Owned by: | nobody | |
|---|---|---|---|
| Component: | Documentation | Version: | 1.8 |
| Severity: | Normal | Keywords: | csv streaming documentation bug |
| Cc: | berker.peksag@… | Triage Stage: | Accepted |
| Has patch: | no | Needs documentation: | no |
| Needs tests: | no | Patch needs improvement: | no |
| Easy pickings: | no | UI/UX: | no |
Hi everyone,
The documentation has an example of how to stream large CSV files.
https://docs.djangoproject.com/en/1.8/howto/outputting-csv/#streaming-large-csv-files
This is great but unfortunately the solution is incorrect (at least in django 1.8 using python 3.4).
Per the documentation for the StreamingHTTPResponse class "It should be given an iterator that yields strings as content."
but csvwriter.writerow returns None, not the result of the file.write call of the file passed to the csvwriter. The Echo class provided in the example was a good idea but it doesn't appear to work.
An alternative solution that does work would be:
def streaming_csv_writer(rows_to_output): memory_file = StringIO() writer = csv.writer(memory_file) for row in rows_to_output: writer.writerow(row) memory_file.seek(0) yield memory_file.read() memory_file.truncate(0)
response = StreamingHTTPResponse(streaming_csv_writer(rows), ...)
I'm happy to patch this myself but I wanted to discuss it first before writing the patch to get some additional opinions and to try to discover a bit of the history of this documentation example (because I have a feeling it must have worked at some time in the past).
Django is a great framework and I'm truly grateful to the maintainers and contributors to the project. You folks rock!
Change History(8)
comment:1 by Philip Zerull, 9 years ago
as an additional note: The documentation for this example is the same in django 1.8 and 1.9. I have not yet confirmed that this issue exists for python2
comment:2 by Simon Charette, 9 years ago
| Triage Stage: | Unreviewed → Accepted |
|---|
comment:3 by Claude Paroz, 9 years ago
When you say it doesn't work, is it that the response is empty or simply that the response is not streamed?
comment:4 by Emett Speer, 9 years ago
Seeing how we are working with "large" amounts of data wouldn't it make it be a good idea to look at heapq to store the list. You can use the heapq library inside generators in Python as well so it could even speed things up a bit more and its supported in all supported versions of Python.
comment:7 by Tim Graham, 9 years ago
The report never said why the example doesn't work. The example works for me on both Python 2.7 and Python 3.5, at least the CSV output looks fine. Is the problem that the response isn't streamed? If so, how do you test that?
comment:8 by Daniel Hepper, 6 years ago
| Resolution: | → invalid |
|---|---|
| Status: | new → closed |
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