Is ListSerializer mishandling multipart/formdata uploads?

[MosheBerman]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

According to the OP on this Stack Overflow question, submitting a list as multipart/formdata, and then running it through a validator returns a list with a string containing all of the fields, instead of a list of the fields.

1. Set up a DFR website.
2. Upload data encoded as multipart/formdata
3. Run it through a ListField validator.

Expected behavior

Data submitted as multipart/formdata and then validated should be returned as a list.

Actual behavior

The output of the validation is an array of a single string.

Notes

I don't know what versions of Python/Django/DRF the OP was using, but I'm using Django 1.9.4, and DRF 3.3.2.

The original conversation was here: http://stackoverflow.com/q/36696285/224988

From the OP:

Users = ['x1','x2']
In my serializer create method I try to iterate over them:

users = validated_data.get('users', None)
for user in users:
    print(user)
    print("===")

The output I receive is:

x1,x2

===

In my answer there, I traced through the ListField and the ListSerializer and guessed (correctly) that the to_representation method in the serializer was flattening the data.

Is this the intended behavior?

Possibly related issues: #3685, #3864, #3970

[xordoquy]

It's a bit to vague for me to process.
As far as I remember, ListSerializer don't work with html forms - might be wrong here, not sure at all.
ListField will work if one had a multiple select widget.
Do you have some code sample we could run ?

[rpkilby]

Was this fixed by #4181?

[xordoquy]

The issue isn't actionnable in its current form and nobody seems to step forward and write a test case for it.
I'll reconsider opening it when provided with a failing test case to demonstrate the issue.