class_docstr: Base class for min-heaps.
  
  A MinHeap stores a collection of key-value pairs ordered by their values.
  It supports querying the minimum pair, inserting a new pair, decreasing the
  value in an existing pair and deleting the minimum pair.
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docstr: Returns the number of key-value pairs in the heap.
docstr_tok: ["Returns","the","number","of","key-value","pairs","in","the","heap","."]
code: def __len__(self):
      """Returns the number of key-value pairs in the heap."""
      return len(self._dict)
  
imports: from heapq import heappop, heappush
  from itertools import count
  import networkx
label_desc: Use image node_id 8 for calling the MinHeap obj's underlying member method code with example usage: obj.__len__() and returns: len