wait, you use context-managers?
Memory leaks?! pfft! my good ol’ Python handles everything for me. Well, we all wish this could have been true, but that’s not the case. Before getting to know context managers, let me highlight the usage of with statement. Let’s see it with the help of a code.
with open('sample.txt', 'w') as file:
file.write('blah')
but what if deadlines are near and you’re throwing the most complex macros at your code to make that deadline possible and exploit Python with a poor choice of code like
file = open('sample.txt')
file.write('blah')
file.close()
Looks good? let’s move on with life and wait for that appraisal?
If you are also thinking like that then you’re in the wrong. There are few but major things that you overlooked that can shoot you in the feet, what if file.write() runs into an error and never reaches file.close()? and that’s how a memory leak is produced because you can never go back to that piece of run because it failed in execution.
Let me break the above code into verbose way of Python and the correct way.
file = open('sample.txt')
try:
file.write('blah')
finally:
file.close()
Now we got the big guns, our near and dear try-catch statements which will help us deal with exceptions and how to handle them and that is the exact way how with statement works under the hood.
Now we shall proceed with context-managers and how we can make our own class-based or function-based with statements. To do so all we need is to add __enter__ & __exit__ dunder methods.
class-based
class Manager:
def __init__(self, name):
self.name = name
def __enter__(self):
self.file = open(self.name, 'w')
return self.file
def __exit__(self, exc_type, exc_val, exc_tb):
if self.file:
self.file.close()
$ usage:
with Manager('sample.txt') as f:
f.write('blah')
function-based
from contextlib import contextmanager
@contextmanager
def manage_file(name: str):
try:
file = open(name, 'w')
finally:
file.close()
$ usage:
with manage_file('sample.txt') as file:
file.write('blah')
and that’s how we make our own context-manager from scratch.
if all of this was overwhelming and you wish not to care about this by yourself; you can use fuckit package in your codebase to handle all the error that has been there since the dawn of mankind and also in the literal sense.
Good to knows
until next time.