code: def _union(w1, w2):
      coeffs = _compute_union(w1, w2)
      return Window(*coeffs)
  
imports: import collections
  from collections.abc import Iterable
  import functools
  import math
  import warnings
  from affine import Affine
  import attr
  import numpy
  from rasterio.errors import WindowError, RasterioDeprecationWarning
  from rasterio.transform import rowcol, guard_transform
label_desc: Use image node_id 5 for calling a global function with example usage: _union(w1, w2) and returns: Window