class_docstr: A pairing heap.
class_docstr_tok: ["A","pairing","heap","."]
code: def pop(self):
      if self._root is None:
          raise nx.NetworkXError("heap is empty.")
      min_node = self._root
      self._root = self._merge_children(self._root)
      del self._dict[min_node.key]
      return (min_node.key, min_node.value)
  
imports: from heapq import heappop, heappush
  from itertools import count
  import networkx
label_desc: Use image node_id 3 for calling the PairingHeap obj's underlying member method code with example usage: obj.pop() and returns: min_node,  min_node