BUG: Fixed strange behaviour of pd.DataFrame.drop() with inplace argu…
closes  #30484

- [x] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

This is my first PR, so pardon me if I did something wrong.

To fix this issue I started by creating a failing test based on the example given by the reporter. After, I fixed the test by removing the "inplace" special methods from add_special_arithmetic_methods, following what was suggested as a comment in the code.
The code that you removed is used in many different files.  If you check the Travis CI logs you will see a list of failures.  Below are a few places where those methods are used:

pandas/tests/frame/test_operators.py
pandas/core/generic.py

You will probably need to either change the current implementation or reimplement those methods elsewhere. Thank you guys! I've run some tests before the PR, so it turns out I was running the wrong ones. I'll take another look and try to find a better solution. I've now fixed the problem by adding a new argument to NDFrame._maybe_update_cacher.

All the test are running fine, but the pipeline fails in building the documentation:
AttributeError: module 'IPython.utils.py3compat' has no attribute 'cast_bytes_py2'

Is this related to something I've done? Can you provide some guidance on how to solve this? Looking further in the azure logs I see that the build is failing because of the following file:

doc/source/user_guide/enhancingperf.rst

I would look through that file and see if anything that you changed is referenced there. Thanks for the remarks and for the review. I'll get back to it as soon as I have time HI @rjfs - sorry to chase you up, just wanted to ask whether you're still working on this :) Hi @MarcoGorelli, no problem!
I've been away during last days, but I'll get back to it during this week. looks good. can you add a note in 1.1, reshaping bug fixes. ping on green. > looks good. can you add a note in 1.1, reshaping bug fixes. ping on green.

It's done, thanks! @rjfs can you rebase once again, azure pipelines are not triggering fro some reason; I think its fixed. > @rjfs can you rebase once again, azure pipelines are not triggering fro some reason; I think its fixed.

still not triggering it seems... /azp run <samp>
Azure Pipelines successfully started running 1 pipeline(s).<br>

</samp> lgtm. let's merge on green. pls merge master and a lint issue: 
```
##[error]./pandas/tests/indexes/timedeltas/test_constructors.py:173:String has a space at the beginning instead of the end of the previous string.
```

ping on green. Hello @rjfs! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-03-26 10:03:05 UTC ping @jreback  thanks @rjfs 