Compose: Only Mount Specific File Extensions

I am not sure if this is possible, but I am wondering if it would be possible to mount only, say, *.py files with the volumes part of the fig.yml.

I am trying to mount a directory that has a python package in it. My Dockefile looks like this:

FROM python:3

ADD . /code/
WORKDIR /code
RUN pip install -r requirements-testing.txt -e .

ENV LC_ALL C.UTF-8
ENV LANG C.UTF-8

The problem is that when I have a fig.yml like this:

python:
  build: .
  volumes:
    - .:/code/

And then run try to run the CLI installed with my Python app, it doesn't work, because pip install -e . creates some directories with the built python package under /code/. Then when I mount my local source code directory over that directory, it removes those build directory and the command fails.

$ fig run python dc-campaign-finance-scraper
Traceback (most recent call last):
  File "/usr/local/bin/dc-campaign-finance-scraper", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python3.4/site-packages/pkg_resources.py", line 2697, in <module>
    working_set.require(__requires__)
  File "/usr/local/lib/python3.4/site-packages/pkg_resources.py", line 669, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/local/lib/python3.4/site-packages/pkg_resources.py", line 572, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: dc-campaign-finance-scraper==0.5.1

So if I could only mount .py files, it wouldn't overwrite all that other stuff. I am not sure if this is remotely possible, and if not, whether you have any tips using fig for python package development/