code: def check_bin_existence(self, chi1_bin, chi2_bin):
          
          bin_range_check = self.bin_range_check
          # Check if this bin actually exists. If not add it
          if ( (chi1_bin < self.min_chi1_bin+bin_range_check) or
               (chi1_bin > self.max_chi1_bin-bin_range_check) or
               (chi2_bin < self.min_chi2_bin+bin_range_check) or
               (chi2_bin > self.max_chi2_bin-bin_range_check) ):
              for temp_chi1 in xrange(chi1_bin-bin_range_check,
                                                     chi1_bin+bin_range_check+1):
                  if temp_chi1 not in self.massbank:
                      self.massbank[temp_chi1] = {}
                      self.bank[temp_chi1] = {}
                  for temp_chi2 in xrange(chi2_bin-bin_range_check,
                                                     chi2_bin+bin_range_check+1):
                      if temp_chi2 not in self.massbank[temp_chi1]:
                          self.massbank[temp_chi1][temp_chi2] = {}
                          self.massbank[temp_chi1][temp_chi2]['mass1s'] =\
                                                                  numpy.array([])
                          self.bank[temp_chi1][temp_chi2] = []
docs: Given indices for bins in chi1 and chi2 space check that the bin
          exists in the object. If not add it. Also check for the existence of
          all bins within +/- self.bin_range_check and add if not present.
  
          Parameters
          -----------
          chi1_bin : int
              The index of the chi1_bin to check
          chi2_bin : int
              The index of the chi2_bin to check