Rectified plot error (#12501)

* Rectified plot error

The plot shown on the page: https://matplotlib.org/tutorials/introductory/usage.html#sphx-glr-tutorials-introductory-usage-py

Will be possible only if plt.show() is outside the loop

* Added corrections in docs as per requirements

* Commented the code block to remove plot rendering

* Added ::

* corrected trailing spaces and bad indentation

* Removed E402