[issue27497] csv module: Add return value to DictWriter.writeheader

[STINNER Victor]

STINNER Victor  added the comment:

I merged PR 12306. Thanks Ashish Nitin Patil for the initial patch, thanks Rémi 
Lapeyre to converting it to a PR, thanks Logan for the initial bug report ;-)

Sadly, this change is a new feature and so cannot be backported to 2.7 or 3.7. 
The workaround is override the method:

def writeheader(self):
header = dict(zip(self.fieldnames, self.fieldnames))
return self.writerow(header)

--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[STINNER Victor]

STINNER Victor  added the comment:


New changeset fce5ff1e18b522cf52379934a6560583d840e7f9 by Victor Stinner (Rémi 
Lapeyre) in branch 'master':
bpo-27497: Add return value to csv.DictWriter.writeheader (GH-12306)
https://github.com/python/cpython/commit/fce5ff1e18b522cf52379934a6560583d840e7f9


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Skip Montanaro]

Skip Montanaro  added the comment:

I think this is ready to go. I added a comment to PR12306. As I am no longer a 
committer, I'm not sure what the next step is.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[MICHAEL BLAHAY]

MICHAEL BLAHAY  added the comment:

Ah ha, so there is. I'm glad this one will get closed out. Sorry for noob 
mistake.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[SilentGhost]

SilentGhost  added the comment:

Michael, there is a up-to-date PR that's waiting for approval.

--
nosy: +SilentGhost

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[MICHAEL BLAHAY]

MICHAEL BLAHAY  added the comment:

I would like to drive this to conclusion since it appears this issue has not 
had any real activity in a while. First thing that needs to be determined is 
whether this enhancement is still desirable. Who can answer this?

--
nosy: +MICHAEL BLAHAY

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Rémi Lapeyre]

Change by Rémi Lapeyre :


--
versions: +Python 3.8 -Python 3.6

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Rémi Lapeyre]

Change by Rémi Lapeyre :


--
pull_requests: +12282

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Ashish Nitin Patil]

Ashish Nitin Patil added the comment:

Thank you Berker & Skip for your review & additional inputs.
I have added a (probably not so good) unittest for testing the newly added 
*return*.
I have also added the corresponding *versionchanged* info to the documentation 
as suggested by Berker.

Will keep these in mind while making a patch next time :)
Kindly let me know if there are any further changes required.

--
Added file: 
http://bugs.python.org/file44372/issue_27497_add_return_to_DictWriter_writeheader_v2.patch

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Skip Montanaro]

Skip Montanaro added the comment:

Also, a change in behavior has to be very carefully considered, even
though it passes all existing test cases (and presumably the one(s)
you'll add). The change may well only be acceptable for the next minor
release of 3.x.

On Mon, Sep 5, 2016 at 7:31 AM, Berker Peksag  wrote:
>
> Berker Peksag added the comment:
>
> Thanks! The patch lacks a test case (you can add it into 
> Lib/test/test_csv.py) and a versionchanged notice in documentation (see 
> http://cpython-devguide.readthedocs.io/en/latest/documenting.html#paragraph-level-markup
>  for details.)
>
> --
> stage: needs patch -> patch review
>
> ___
> Python tracker 
> 
> ___

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Berker Peksag]

Berker Peksag added the comment:

Thanks! The patch lacks a test case (you can add it into Lib/test/test_csv.py) 
and a versionchanged notice in documentation (see 
http://cpython-devguide.readthedocs.io/en/latest/documenting.html#paragraph-level-markup
 for details.)

--
stage: needs patch -> patch review

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Ashish Nitin Patil]

Ashish Nitin Patil added the comment:

Also, I noticed in the documentation for `csv.DictWriter` 
(https://docs.python.org/3/library/csv.html#csv.DictWriter.writeheader) does 
not contain the following line -
 to the writer's file object, formatted according to the current dialect.
Although it is there for the other 2 methods (`writerow` & `writerows`) and 
since `writeheader` uses `writerow` in turn, I believe the said line should be 
included for the `writeheader` documentation as well. I have created another 
patch with both the changes. I ran the Doc build (make html) and have checked 
the addition of the said lines looks good & does not break anything.

I can make another thread if required, if you feel both the changes can't be 
accommodated in the same issue.

--
Added file: 
http://bugs.python.org/file44365/issue_27497_add_return_to_DictWriter_writeheader_with_documentation_changes.patch

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Ashish Nitin Patil]

Ashish Nitin Patil added the comment:

Hi, I have added the "return" to the writeheader method. I ran the tests for 
the csv library (./python -m test -v test_csv) and got no errors (Ran 101 tests 
in 0.322s; 1 test OK.).

Kindly review the patch.

--
keywords: +patch
nosy: +ashishnitinpatil
Added file: 
http://bugs.python.org/file44364/issue_27497_add_return_to_DictWriter_writeheader.patch

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[STINNER Victor]

STINNER Victor added the comment:

I'm now ok to add the return, but only in Python 3.6. It would be a minor new 
"feature".

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Logan]

Logan added the comment:

@berker.peksag: Good catch, thank you.  In my code base I'm using a slightly 
different implementation which does use an iterator, so I didn't even catch 
that the default django example was incorrect.

@skip.montanaro: That is exactly the one-liner I'm currently using.  Thank you 
for documenting it here in case anyone else is looking for the same.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Skip Montanaro]

Skip Montanaro added the comment:

I agree writeheader() should have returned the value of writerow(), but have no 
opinion on the more esoteric stuff you're discussing. I think you could argue 
that adding the "return" would be a bug fix.

Personally, I long ago got in the habit of using the writerow(dict(zip(fh, 
fh))) idiom, didn't catch on at the time that writeheader() was even available 
in 2.7, and still just use the idiom most of the time. It's a one-liner. The OP 
could easily use that in contexts where writeheader() doesn't do the right 
thing.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Berker Peksag]

Berker Peksag added the comment:

By the way, there is an open ticket about changing the recipe in Django 
documentation: https://code.djangoproject.com/ticket/26040

--
nosy: +berker.peksag

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[STINNER Victor]

STINNER Victor added the comment:

Oh. I missed the django recipe to implement "streaming csv". It uses an
Echo object, its write() method returns its parameter.

This recipe looks like an abuse of the API, but I understand that there is
a need for a kind of "partial write": give control to I/O to the caller.

Maybe we should extend the API?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[R. David Murray]

R. David Murray added the comment:

It doesn't make sense when the return value is that provided by io.write.  It 
does make sense in the context of the linked example (a psuedo-file object).  
However, it *is* an undocumented API, even if people are using it.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Raymond Hettinger]

Raymond Hettinger added the comment:

It is a bit irritating to have this small API inconsistency, but I'm a little 
wary of propagating this undocumented and untested behavior especially given 
Victor's concern about whether it makes any sense in this context.

Skip, what do you think?

--
assignee:  -> skip.montanaro
nosy: +rhettinger, skip.montanaro

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[R. David Murray]

R. David Murray added the comment:

It isn't documented that writer.writeline returns anything, but what it 
actually returns is whatever the write method of the underlying file object 
returns.  Obviously (given the linked example), this fact is being used.  There 
is value in consistency, so I think we should make this change.

--
nosy: +r.david.murray

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[STINNER Victor]

STINNER Victor added the comment:

It doesn't seem right to me.

The writer should be blocking: write *all* data, don't use partial write.

Supporting partial write (non-blocking files) requires more changes, and it 
isn't worth it.

Here the problem is that the function doesn't support partial write. Each time, 
it tries to write the full content.

What is your use case?

--
nosy: +haypo

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Zachary Ware]

Zachary Ware added the comment:

This seems like a reasonable request, but could only be done in 3.6 as it would 
be a new feature.

--
keywords: +easy
nosy: +zach.ware
stage:  -> needs patch
versions:  -Python 3.5

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27497] csv module: Add return value to DictWriter.writeheader

[Logan]

New submission from Logan:

Currently, DictWriter.writeheader() is defined like:

def writeheader(self):
header = dict(zip(self.fieldnames, self.fieldnames))
self.writerow(header)

It would be useful to have it return the value of writerow():

def writeheader(self):
header = dict(zip(self.fieldnames, self.fieldnames))
return self.writerow(header)

This would useful because:
1) It would match the behavior of DictWriter.writerow
2) It would enable DictWriter.writeheader to be used in within a generator 
function (ala 
https://docs.djangoproject.com/en/1.9/howto/outputting-csv/#streaming-large-csv-files)

--
messages: 270248
nosy: lsowen
priority: normal
severity: normal
status: open
title: csv module: Add return value to DictWriter.writeheader
type: enhancement
versions: Python 3.5, Python 3.6

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com