code: def __iadd__(self, other):
      if not isinstance(other, TupleVariation):
          return NotImplemented
      deltas1 = self.coordinates
      length = len(deltas1)
      deltas2 = other.coordinates
      if len(deltas2) != length:
          raise ValueError(
              "cannot sum TupleVariation deltas with different lengths"
          )
      # 'None' values have different meanings in gvar vs cvar TupleVariations:
      # within the gvar, when deltas are not provided explicitly for some points,
      # they need to be inferred; whereas for the 'cvar' table, if deltas are not
      # provided for some CVT values, then no adjustments are made (i.e. None == 0).
      # Thus, we cannot sum deltas for gvar TupleVariations if they contain
      # inferred inferred deltas (the latter need to be computed first using
      # 'calcInferredDeltas' method), but we can treat 'None' values in cvar
      # deltas as if they are zeros.
      if self.getCoordWidth() == 2:
          for i, d2 in zip(range(length), deltas2):
              d1 = deltas1[i]
              try:
                  deltas1[i] = (d1[0] + d2[0], d1[1] + d2[1])
              except TypeError:
                  raise ValueError(
                      "cannot sum gvar deltas with inferred points"
                  )
      else:
          for i, d2 in zip(range(length), deltas2):
              d1 = deltas1[i]
              if d1 is not None and d2 is not None:
                  deltas1[i] = d1 + d2
              elif d1 is None and d2 is not None:
                  deltas1[i] = d2
              # elif d2 is None do nothing
      return self
  
imports: from fontTools.misc.fixedTools import fixedToFloat, floatToFixed, floatToFixedToStr, strToFixedToFloat, otRound
  from fontTools.misc.textTools import safeEval
  import array
  from collections import Counter, defaultdict
  import io
  import logging
  import struct
  import sys
label_desc: Use image node_id 27 for calling the TupleVariation obj's underlying member method code with example usage: obj.__iadd__(other) and returns: self, NotImplemented