code: def _kl_poisson_poisson(dist1, dist2):
      return (
          dist1.lam * (dist1._log_lam - dist2._log_lam)
          - dist1.lam
          + dist2.lam
      )
  
imports: import chainer
  from chainer.backends import cuda
  from chainer import distribution
  from chainer.functions.math import exponential
  from chainer.functions.math import lgamma
  from chainer import utils
  from chainer.utils import cache
label_desc: Use image node_id 1 for calling a global function with example usage: _kl_poisson_poisson(dist1, dist2) and returns: unknown