class_docstr: Immutable dictionary used to represent a Fermi word, a product of fermionic creation and
  annihilation operators, that can be constructed from a standard dictionary.
  
  The keys of the dictionary are tuples of two integers. The first integer represents the
  position of the creation/annihilation operator in the Fermi word and the second integer
  represents the orbital it acts on. The values of the dictionary are one of ``'+'`` or ``'-'``
  symbols that denote creation and annihilation operators, respectively. The operator
  :math:`a^{\dagger}_0 a_1` can then be constructed as
  
  >>> w = FermiWord({(0, 0) : '+', (1, 1) : '-'})
  >>> w
  a⁺(0) a(1)
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docstr: Terminal representation of a FermiWord
docstr_tok: ["Terminal","representation","of","a","FermiWord"]
code: def __repr__(self):
      r"""Terminal representation of a FermiWord"""
      return str(self)
  
imports: import re
  from copy import copy
  from numbers import Number
  from numpy import ndarray
  import pennylane
label_desc: Use image node_id 12 for calling the FermiWord obj's underlying member method code with example usage: obj.__repr__() and returns: str