class_docstr: The custom IPython displayhook to replace sys.displayhook.
  
  This class does many things, but the basic idea is that it is a callable
  that gets called anytime user code returns a value.
class_docstr_tok: ["The","custom","IPython","displayhook","to","replace","sys.displayhook",".","This","class","does","many","things",",","but","the","basic","idea","is","that","it","is","a","callable","that","gets","called","anytime","user","code","returns","a","value","."]
docstr: Check if the user has set the '_' variable by hand.
docstr_tok: ["Check","if","the","user","has","set","the","'","_","'","variable","by","hand","."]
code: def check_for_underscore(self):
      """Check if the user has set the '_' variable by hand."""
      # If something injected a '_' variable in __builtin__, delete
      # ipython's automatic one so we don't clobber that.  gettext() in
      # particular uses _, so we need to stay away from it.
      if "_" in builtin_mod.__dict__:
          try:
              del self.shell.user_ns["_"]
          except KeyError:
              pass
  
imports: from __future__ import print_function
  import sys
  import io
  import tokenize
  from traitlets.config.configurable import Configurable
  from IPython.utils.py3compat import builtin_mod, cast_unicode_py2
  from traitlets import Instance, Float
  from warnings import warn
label_desc: Use image node_id 3 for calling the DisplayHook obj's underlying member method code with example usage: obj.check_for_underscore() without return types