fix pylint warning '(pointless-string-statement) String statement has no effect'

Python doesn't support docstring for variables directly. Where
appropriate Sphinx style for docstrings for variables is used
'#: some-docstring'

fix error __init__ method from base class is not called

fix more than one statement on a single line

fix ungrouped imports from package X

fix unnecessary lambda and enable corresponding pylint check

fix wrong-import-order. first standard modules are imported, then others