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

CharField().to_internal_value(0.00001)

Expected behavior

Either a validation error or the returned value being exactly '0.00001'.

Actual behavior

The returned value is '1e-05' due to float formatting in the cast.

Something similar would also happen with floats with a lot of decimals, since python will not cast into a string with more than 16 decimals.

Being lenient and accepting integers as a valid input for a CharField is fine, but accepting floats causes this problem.
This is a corner case, but I think it should be a configurable behavior.

I also couldn't find anything documenting this behavior other than the pull request that added it. #4380