为什么Python 3找不到安装的软件包（例如BeautifulSoup4）？

Question

Using Ubuntu 16.04 with Python 3.5 I get import errors for some packages, eg 'BeautifulSoup4' or 'requests'. Both libraries are installed from the Ubuntu repositories:

$ dpkg --get-selections | grep -E "python3-req|python3-bs"
python3-bs4                         install
python3-requests                    install

Yet I get "ImportError: no module named 'bs4'/'requests'".

$ python3 -c "import bs4"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named 'bs4'

Only when I (additionally!) install those libraries via pip3 it works. The documentation of BeautifulSoup says to install it as "python3-bs4" via apt. Why does it only work with the pip3 method? What's the purpose of the python3-bs4/python3-requests packages?

Answer 1

I was able to resolve the issue.

I'm still not quite sure what was the exact problem, but I suspect that pip3 and apt confused each other about what was actually installed. pip3 also listed several python packages which were installed via apt .

I removed/purged everything via apt that was recognized by pip3 list and also purged pip3. Then I apt install --reinstall the packages that gave me trouble previously: python3-bs4 and python3-requests. The requests library still didn't work because it missed the packages python3-six , python3-chardet and python3-urllib3 which where reported as already installed by apt. A apt install --reinstall fixed this as well. And then it worked!