Why My Python Debugger Failed on Ubuntu and How I Fixed It

I wrote a Python data‑conversion script that runs but needed debugging, and when I launched PyCharm’s debugger I got an ImportError: No module named parse.

The traceback showed that pydev_imports.py tried to import urllib.parse, which exists only in Python 3, while I was running Python 2.7.

/usr/bin/python2.7 /buildtools/pycharm-2017.1/helpers/pydev/pydevd.py --multiproc --qt-support --client 127.0.0.1 --port 36360 --file /study/python/zookeeper/app.py
Traceback (most recent call last):
  File "/buildtools/pycharm-2017.1/helpers/pydev/pydevd.py", line 17, in <module>
    from _pydev_bundle import pydev_imports, pydev_log
  File "/buildtools/pycharm-2017.1/helpers/pydev/_pydev_bundle/pydev_imports.py", line 59, in <module>
    from urllib.parse import quote, quote_plus, unquote_plus #@UnresolvedImport
ImportError: No module named parse

Initially I blamed PyCharm, upgraded it, but the problem persisted. I realized the issue stemmed from the code in pydev_imports.py that conditionally imports urllib for Python 2 and urllib.parse for Python 3.

After removing Python 3 from the system the error disappeared, but the Ubuntu desktop became unusable: the panel and menu vanished, leaving only a SlickEdit icon.

Using Ctrl+Alt+F6 to switch to a TTY, I restored the Unity desktop with the following commands:

sudo apt-get install dconf-tools
dconf reset -f /org/compiz/
setsid unity
unity --reset-icons

After reboot the desktop returned, though some applications like Update‑Manager, gedit, and the Sogou input method were missing; I reinstalled them with dpkg -i sogoupinyin_2.1.0.0082_amd64.deb and switched to Atom.

Finally I discovered a stray urllib.py file in my project directory; deleting it allowed PyCharm to debug correctly. The episode highlighted how a name clash with a standard library module can break debugging and how removing Python 3 can cripple an Ubuntu system.