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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