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#!/usr/bin/env python
# Copyright (C) 2010 Google Inc. All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following disclaimer
# in the documentation and/or other materials provided with the
# distribution.
# * Neither the name of Google Inc. nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""
Package that implements a stream wrapper that has 'meters' as well as
regular output. A 'meter' is a single line of text that can be erased
and rewritten repeatedly, without producing multiple lines of output. It
can be used to produce effects like progress bars.
"""
class MeteredStream:
"""This class is a wrapper around a stream that allows you to implement
meters.
It can be used like a stream, but calling update() will print
the string followed by only a carriage return (instead of a carriage
return and a line feed). This can be used to implement progress bars and
other sorts of meters. Note that anything written by update() will be
erased by a subsequent update(), write(), or flush()."""
def __init__(self, verbose, stream):
"""
Args:
verbose: whether update is a no-op
stream: output stream to write to
"""
self._dirty = False
self._verbose = verbose
self._stream = stream
self._last_update = ""
def write(self, txt):
"""Write text directly to the stream, overwriting and resetting the
meter."""
if self._dirty:
self.update("")
self._dirty = False
self._stream.write(txt)
def flush(self):
"""Flush any buffered output."""
self._stream.flush()
def update(self, str):
"""Write an update to the stream that will get overwritten by the next
update() or by a write().
This is used for progress updates that don't need to be preserved in
the log. Note that verbose disables this routine; we have this in
case we are logging lots of output and the update()s will get lost
or won't work properly (typically because verbose streams are
redirected to files.
TODO(dpranke): figure out if there is a way to detect if we're writing
to a stream that handles CRs correctly (e.g., terminals). That might
be a cleaner way of handling this.
"""
if self._verbose:
return
# Print the necessary number of backspaces to erase the previous
# message.
self._stream.write("\b" * len(self._last_update))
self._stream.write(str)
num_remaining = len(self._last_update) - len(str)
if num_remaining > 0:
self._stream.write(" " * num_remaining + "\b" * num_remaining)
self._last_update = str
self._dirty = True
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