old_contents: # Copyright (c) 2012 Giorgos Verigakis <verigak@gmail.com>
  #
  # Permission to use, copy, modify, and distribute this software for any
  # purpose with or without fee is hereby granted, provided that the above
  # copyright notice and this permission notice appear in all copies.
  #
  # THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  # ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  # OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  
  from __future__ import print_function
  
  
  class WriteMixin(object):
      def __init__(self, message=None, **kwargs):
          super(WriteMixin, self).__init__(**kwargs)
          self._width = 0
          if message:
              self.message = message
  
          if self.file.isatty():
              print(self.message, end='', file=self.file)
              self.file.flush()
  
      def write(self, s):
          if self.file.isatty():
              b = '\b' * self._width
              print(b + s.ljust(self._width), end='', file=self.file)
              self._width = max(self._width, len(s))
              self.file.flush()
  
  
  class WritelnMixin(object):
      def __init__(self, message=None, **kwargs):
          super(WritelnMixin, self).__init__(**kwargs)
          self.max_line_width = 0
          if message:
              self.message = message
  
      def writeln(self, line):
          if not self.file.isatty():
              return
          if len(line) > self.max_line_width:
              self.max_line_width = len(line)
          else:
              line += ' ' * (self.max_line_width - len(line))     # Add padding
  
          print('\r' + line, end='', file=self.file)
          self.file.flush()
  
      def finish(self):
          if self.file.isatty():
              print(file=self.file)
  
new_contents: # Copyright (c) 2012 Giorgos Verigakis <verigak@gmail.com>
  #
  # Permission to use, copy, modify, and distribute this software for any
  # purpose with or without fee is hereby granted, provided that the above
  # copyright notice and this permission notice appear in all copies.
  #
  # THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  # ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  # OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  
  from __future__ import print_function
  
  
  class WriteMixin(object):
      def __init__(self, message=None, **kwargs):
          super(WriteMixin, self).__init__(**kwargs)
          self._width = 0
          if message:
              self.message = message
  
          if self.file.isatty():
              print(self.message, end='', file=self.file)
              self.file.flush()
  
      def write(self, s):
          if self.file.isatty():
              b = '\b' * self._width
              print(b + s.ljust(self._width), end='', file=self.file)
              self._width = max(self._width, len(s))
              self.file.flush()
  
  
  class WritelnMixin(object):
      def __init__(self, message=None, **kwargs):
          super(WritelnMixin, self).__init__(**kwargs)
          if message:
              self.message = message
  
  
      def clearln(self):
          if self.file.isatty():
              print('\r\x1b[K', end='', file=self.file)
  
      def writeln(self, line):
          if self.file.isatty():
              self.clearln()
              print(line, end='', file=self.file)
              self.file.flush()
  
      def finish(self):
          if self.file.isatty():
              print(file=self.file)
  
subject: Use ANSI clear line instead of tracking line width