[gourav]

I tried that and even that shows the same error.

I also tried reinstalling, and this time I noticed that it's giving the error at the time of installation itself:

____________________ WARNING ____________________
Setting up completion failed with error:
__________________________________________________


        Traceback (most recent call last):
          File "calibre/linux.py", line 832, in setup_completion
          File "calibre/linux.py", line 574, in write_completion
          File "bypy-importer.py", line 154, in exec_module
          File "calibre/gui2/__init__.py", line 16, in <module>
        ImportError: cannot import name 'QApplication' from 'PyQt5.Qt' (/opt/calibre/lib/calibre-extensions/PyQt5.Qt.so)

Setting up desktop integration...

____________________ WARNING ____________________
Setting up desktop integration failed with error:
__________________________________________________


        Traceback (most recent call last):
          File "calibre/linux.py", line 900, in setup_desktop_integration
          File "calibre/linux.py", line 885, in install_icons
          File "calibre/linux.py", line 875, in install_single_icon
          File "calibre/linux.py", line 1219, in render_img
        ImportError: cannot import name 'QImage' from 'PyQt5.Qt' (/opt/calibre/lib/calibre-extensions/PyQt5.Qt.so)