[docs] [issue15204] Deprecate the 'U' open mode

Roundup Robot added the comment: New changeset 2d5544afb510 by R David Murray in branch 'default': whatsnew: 'U' mode deprecation (#15204). http://hg.python.org/cpython/rev/2d5544afb510 ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue15204> _______________________________________