csvkit: in2csv: "ImportWarning: can't resolve package from __spec__ or __package__"

After installing csvkit using pip (under 4.14.9-2-MANJARO Linux with Python 3.6.4), and running in2csv, I got a bunch of warnings like these:

$ in2csv
/usr/lib/python3.6/importlib/_bootstrap.py:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
/usr/lib/python3.6/importlib/_bootstrap.py:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
/usr/lib/python3.6/importlib/_bootstrap.py:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
... [about 20 of the same omitted]
/usr/lib/python3.6/importlib/_bootstrap.py:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
usage: in2csv [-h] [-d DELIMITER] [-t] [-q QUOTECHAR] [-u {0,1,2,3}] [-b]
              [-p ESCAPECHAR] [-z FIELD_SIZE_LIMIT] [-e ENCODING] [-L LOCALE]
              [-S] [--blanks] [--date-format DATE_FORMAT]
              [--datetime-format DATETIME_FORMAT] [-H] [-K SKIP_LINES] [-v]
              [-l] [--zero] [-V] [-f FILETYPE] [-s SCHEMA] [-k KEY] [-n]
              [--sheet SHEET] [--write-sheets WRITE_SHEETS] [-y SNIFF_LIMIT]
              [-I]
              [FILE]

The script works (when provided a file), but generates these warnings every time.

Environment:

$ pip freeze
agate==1.6.0
agate-dbf==0.2.0
agate-excel==0.2.1
agate-sql==0.5.2
appdirs==1.4.3
awscli==1.14.26
Babel==2.5.3
Beaker==1.8.1
beautifulsoup4==4.6.0
bigml==4.14.0
bigmler==3.16.0
bleach==2.1.1
botocore==1.8.32
catfish==1.4.2
certifi==2018.1.18
chardet==3.0.4
colorama==0.3.9
csvkit==1.0.2
cycler==0.10.0
dbfread==2.0.7
decorator==4.2.1
docopt==0.6.2
docutils==0.14
entrypoints==0.2.3
et-xmlfile==1.0.1
future==0.16.0
gufw==17.10.0
html5lib==1.0b10
idna==2.6
ipykernel==4.6.1
ipython==6.2.1
ipython-genutils==0.2.0
ipywidgets==6.0.0
isodate==0.6.0
jdcal==1.3
jedi==0.11.1
Jinja2==2.10
jmespath==0.9.3
joblib==0.11
jsonschema==2.6.0
jupyter-client==5.1.0
jupyter-console==5.2.0
jupyter-contrib-core==0.3.3
jupyter-contrib-nbextensions==0.3.3
jupyter-core==4.4.0
jupyter-highlight-selected-word==0.1.0
jupyter-latex-envs==1.4.0
jupyter-nbextensions-configurator==0.2.8
keyutils==0.5
leather==0.3.3
lightdm-gtk-greeter-settings==1.2.2
louis==3.4.0
lxml==4.1.1
Mako==1.0.7
MarkupSafe==1.0
matplotlib==2.1.0
menulibre==2.1.3
mistune==0.8.3
mugshot==0.3.2
nbconvert==5.3.1
nbformat==4.4.0
notebook==5.2.2
npyscreen==4.10.5
numpy==1.13.3
olefile==0.44
openpyxl==2.5.0
packaging==16.8
pacman-mirrors==4.7.0
pandas==0.21.0
pandocfilters==1.4.2
parsedatetime==2.4
parso==0.1.1
pexpect==4.3.0
pickleshare==0.7.4
Pillow==4.3.0
prettytable==0.7.2
prompt-toolkit==1.0.15
psutil==5.4.1
ptyprocess==0.5.2
pyasn1==0.4.2
pycairo==1.15.4
Pygments==2.2.0
pygobject==3.26.1
pyparsing==2.2.0
python-dateutil==2.6.1
python-distutils-extra==2.39
python-sane==2.8.3
python-slugify==1.2.4
pytimeparse==1.1.7
pytz==2017.3
pyxdg==0.25
PyYAML==3.12
pyzmq==16.0.3
reportlab==3.4.0
requests==2.18.4
requests-toolbelt==0.8.0
rsa==3.4.2
ruamel.yaml==0.15.35
s3transfer==0.1.12
scikit-learn==0.19.1
scipy==1.0.0
simplegeneric==0.8.1
six==1.11.0
skll==1.5
SQLAlchemy==1.2.2
team==1.0
terminado==0.8.1
testpath==0.3.1
tornado==4.5.2
traitlets==4.3.2
udiskie==1.7.3
Unidecode==1.0.22
urllib3==1.22
virtualenv==15.1.0
wcwidth==0.1.7
webencodings==0.5.1
widgetsnbextension==2.0.0
xlrd==1.1.0