<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def is_insert_grad_of_statement(node):
 """Check whether a context manager calls `insert_grad_of`. Args: node: The context manager node. Returns: Whether or not this node contains `insert_grad_of` calls. Raises: ValueError: If the `insert_grad_of` calls are mixed with other calls. """

  tangent_calls = [anno.getanno(item.context_expr, 'func', None)
                   is utils.insert_grad_of for item in node.items]
  if all(tangent_calls):
    return True
  elif any(tangent_calls):
    raise ValueError
  else:
    return False