code: def popleft(self):
      assert len(self) > 0
      self.priority_sums.popleft()
      self.priority_mins.popleft()
      return self.data.popleft()
  
imports: import collections
  import numpy
  from chainerrl.misc.random import sample_n_k
label_desc: Use image node_id 4 for calling the PrioritizedBuffer obj's underlying member method code with example usage: obj.popleft() and returns: self