py3: don?t subscript socket.error On Python 2, socket.error was subscriptable. On Python 3, socket.error is an alias to OSError and is not subscriptable. The except block passes the exception to self.send_error(). This fails on both Python 2 (if it was executed) and Python 3, as it expects a string. Getting the attribute .strerror works on Python 2 and Python 3, and has the same effect as the previous code on Python 2.

#require black test-repo

Black needs the real USERPROFILE in order to run on Windows
#if msys
  $ USERPROFILE="$REALUSERPROFILE"
  $ export USERPROFILE
#endif

  $ cd $RUNTESTDIR/..
  $ black --check --diff `hg files 'set:(**.py + grep("^#!.*python")) - mercurial/thirdparty/**'`