class_docstr: Function hook that prints debug information.
  
  This function hook outputs the debug information of input arguments of
  ``forward`` and ``backward`` methods involved in the hooked functions
  at preprocessing time (that is, just before each method is called).
  
  Unlike simple "debug print" technique, where users insert print functions
  at every function to be inspected, we can show the information
  of all functions involved with single ``with`` statement.
  
  Further, this hook enables us to show the information of
  ``backward`` methods without inserting print functions into
  Chainer's library code.
  
  Args:
      sep: *(deprecated since v4.0.0)* Ignored.
      end: Character to be added at the end of print function.
      file: Output file_like object that that redirect to.
      flush: If ``True``, this hook forcibly flushes the text stream
          at the end of preprocessing.
  
  .. admonition:: Example
  
      The basic usage is to use it with ``with`` statement.
  
      >>> from chainer import function_hooks
      >>> l = L.Linear(10, 10)
      >>> x = chainer.Variable(np.zeros((1, 10), np.float32))
      >>> with chainer.function_hooks.PrintHook():
      ...     y = l(x)
      ...     z = F.sum(y)
      ...     z.backward() # doctest:+SKIP
  
      In this example, ``PrintHook`` shows the debug information of
      forward propagation of ``LinearFunction`` (which is implicitly
      called by ``l``) and ``Sum`` (called by ``F.sum``)
      and backward propagation of ``z`` and ``y``.
code: def forward_preprocess(self, function, in_data):
      self._process(function, in_data)
  
file_path: chainer/chainer/function_hooks/debug_print.py
imports: import sys
  import warnings
  from chainer import backend
  from chainer import function_hook
  from chainer import variable
label_desc: Use image node_id 4 for calling the PrintHook obj's underlying member method code with example usage: obj.forward_preprocess(function, in_data) without return types