Question

What are the real performance advantages of using

with open(__file__, 'r') as f:

instead of using:

open(__file__,'r')

in Python 3 for both writing and reading files?

Answer 1

What the with statement basically does is take advantage of two new magic keywords on an object: __enter__ and __exit__ to implement automatic cleanup (c++ destructors, .net IDisposable, etc). So what effectively happens is as follows:

file = open(__file__, 'r')
try:
  # your code here
finally: file.close()

Feel free to read a bit more about the actual implementation in pep-0343