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