need help with solution-checker function

[Windspar]

NumPy can give you the best of both worlds. If you can't decide.

import numpy as np

# Flat array
grid = np.array([str(i) for i in range(9)])
# Reshape 3 by 3 grid
grid.shape = (3,3)
print(grid)
# still let you use it as a flat array
grid.flat[3] = 'X'
print()
print(grid)