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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def griditer(x, y, ncol, nrow=None, step=1):
 """ Iterate through a grid of tiles. Args: x (int):
 x start-coordinate y (int):
 y start-coordinate ncol (int):
 number of tile columns nrow (int):
 number of tile rows. If not specified, this defaults to ncol, s.t. a quadratic region is generated step (int):
 clear. Analogous to range(). Yields: Tuple: all tuples (x, y) in the region delimited by (x, y), (x + ncol, y + ncol). """

    if nrow is None:
        nrow = ncol
    yield from itertools.product(range(x, x + ncol, step),
                                 range(y, y + nrow, step))