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# encoding: utf-8
"""
A context manager for handling sys.displayhook.
Authors:
* Robert Kern
* Brian Granger
"""
#-----------------------------------------------------------------------------
# Copyright (C) 2008-2011 The IPython Development Team
#
# Distributed under the terms of the BSD License. The full license is in
# the file COPYING, distributed as part of this software.
#-----------------------------------------------------------------------------
#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------
import sys
from traitlets.config.configurable import Configurable
from traitlets import Any
#-----------------------------------------------------------------------------
# Classes and functions
#-----------------------------------------------------------------------------
class DisplayTrap(Configurable):
"""Object to manage sys.displayhook.
This came from IPython.core.kernel.display_hook, but is simplified
(no callbacks or formatters) until more of the core is refactored.
"""
hook = Any()
def __init__(self, hook=None):
super(DisplayTrap, self).__init__(hook=hook, config=None)
self.old_hook = None
# We define this to track if a single BuiltinTrap is nested.
# Only turn off the trap when the outermost call to __exit__ is made.
self._nested_level = 0
def __enter__(self):
if self._nested_level == 0:
self.set()
self._nested_level += 1
return self
def __exit__(self, type, value, traceback):
if self._nested_level == 1:
self.unset()
self._nested_level -= 1
# Returning False will cause exceptions to propagate
return False
def set(self):
"""Set the hook."""
if sys.displayhook is not self.hook:
self.old_hook = sys.displayhook
sys.displayhook = self.hook
def unset(self):
"""Unset the hook."""
sys.displayhook = self.old_hook
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