class_docstr: This class represents an abstract partition.
  
  A partition is a set of disjoint sets whose union equals a given set.
  
  See Also
  ========
  
  sympy.utilities.iterables.partitions,
  sympy.utilities.iterables.multiset_partitions
docstr: Gets the rank of a partition.
  
  Examples
  ========
  
  >>> from sympy.combinatorics import Partition
  >>> a = Partition([1, 2], [3], [4, 5])
  >>> a.rank
  13
code: def rank(self):
      """
      Gets the rank of a partition.
  
      Examples
      ========
  
      >>> from sympy.combinatorics import Partition
      >>> a = Partition([1, 2], [3], [4, 5])
      >>> a.rank
      13
      """
      if self._rank is not None:
          return self._rank
      self._rank = RGS_rank(self.RGS)
      return self._rank
  
imports: from sympy.core import Basic, Dict, sympify, Tuple
  from sympy.core.numbers import Integer
  from sympy.core.sorting import default_sort_key
  from sympy.core.sympify import _sympify
  from sympy.functions.combinatorial.numbers import bell
  from sympy.matrices import zeros
  from sympy.sets.sets import FiniteSet, Union
  from sympy.utilities.iterables import flatten, group
  from sympy.utilities.misc import as_int
  from collections import defaultdict
label_desc: Use image node_id 8 for calling the Partition obj's underlying member method code with example usage: obj.rank() and returns: self, self