code: def is_call(self, call):
          
  
          # guard conditions
          if not len(call) == self.shape[-1]:
              raise ValueError('invalid call ploidy: %s', repr(call))
  
          if self.ndim == 2:
              call = np.asarray(call)[np.newaxis, :]
          else:
              call = np.asarray(call)[np.newaxis, np.newaxis, :]
          out = np.all(self.values == call, axis=-1)
  
          # handle mask
          if self.mask is not None:
              out &= ~self.mask
  
          return out
docs: Locate genotypes with a given call.
  
          Parameters
          ----------
          call : array_like, int, shape (ploidy,)
              The genotype call to find.
  
          Returns
          -------
          out : ndarray, bool, shape (n_variants, n_samples)
              Array where elements are True if the genotype is `call`.
  
          Examples
          --------
  
          >>> import allel
          >>> g = allel.GenotypeArray([[[0, 0], [0, 1]],
          ...                          [[0, 1], [1, 1]],
          ...                          [[0, 2], [-1, -1]]])
          >>> g.is_call((0, 2))
          array([[False, False],
                 [False, False],
                 [ True, False]])
          >>> v = g[:, 0]
          >>> v
          <GenotypeVector shape=(3, 2) dtype=int64>
          0/0 0/1 0/2
          >>> v.is_call((0, 2))
          array([False, False,  True])