class_docstr: Optionally wrap inside `context_manager` if condition is `True`.
code: def __enter__(self):
      if self.condition:
          return self.context_manager.__enter__()
  
imports: import functools
  import math
  import numbers
  import random
  import sys
  import timeit
  import warnings
  from collections import defaultdict
  from contextlib import contextmanager
  from itertools import zip_longest
  import numpy
  import torch
  from pyro.poutine.util import site_is_subsample
label_desc: Use image node_id 2 for calling the optional obj's underlying member method code with example usage: obj.__enter__() and returns: self