Git has unfortunately-named nevertheless handy tool for exploring historical file data -- git blame. There's an alternative GUI implementation for Mercurial thg annotate, a part of Tortoise Hg suite.
Annotate tool works exactly the same as blame, just specify a file name i.e. thg annotate setup.py and a window will pop up with revision list, diff and annotate options.
Right-clicking on diff window and selecting Annotate Options brings up possible annotation selection that for some reason aren't selected by default: 'Show Author', 'Show Date' and 'Show Revision'.
StackOverflow discussion -- http://stackoverflow.com/questions/2228188/finding-the-author-of-a-line-of-code-in-mercurial
Debian Package (stretch) -- https://packages.debian.org/stretch/tortoisehg
Project Page -- https://www.mercurial-scm.org/wiki/TortoiseHg