File open and close in python

Question

I have read that when a file is opened using the below format

with open(filename) as f: 

#My Code 

f.close()

explicit closing of file is not required. Can someone explain why is it so? Also if someone does explicitly close the file, will it have any undesirable effect?

Answer 1

 To open and close a file in Python you leave the nested block, Python automatically calls f.close() for you.

It doesn't matter whether you leave by just falling off the bottom, or calling break/continue/return to jump out of it, or raise an exception; no matter how you leave that block. It always knows you're leaving, so it always closes the file.*

To know more about this you can have a look at the following video tutorial:-