plt.grid

plt.grid(b=None, which='major', axis='both', **kwargs)
Turn the axes grids on or off.

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plt.grid(b=True, which='major', axis='y')

Set the axes grids on or off; *b* is a boolean. (For MATLAB
compatibility, *b* may also be a string, 'on' or 'off'.)

If *b* is *None* and ``len(kwargs)==0``, toggle the grid state. If
*kwargs* are supplied, it is assumed that you want a grid and *b*
is thus set to *True*.

*which* can be 'major' (default), 'minor', or 'both' to control
whether major tick grids, minor tick grids, or both are affected.

*axis* can be 'both' (default), 'x', or 'y' to control which
set of gridlines are drawn.

*kwargs* are used to set the grid line properties, e.g.,::

ax.grid(color='r', linestyle='-', linewidth=2)