(21)CONTEXT MANAGERS:

Context managers are great tool for resource management. they allow you to allocate and release resources precisely when you want to.

for example:

with open('notes.txt', 'w') as f:

    f.write('some todo...')    

output = creates a notes.txt file and types the txt 'some todo'.

1.Handling exceptions:

You can handle an exception automatically without needing to fix it with code.

for example:

class ManagedFile:

    def __init__(self, filename):

        print('init', filename)

        self.filename = filename

    def __enter__(self):

        print('enter')

        self.file = open(self.filename, 'w')

        return self.file

    def __exit__(self, exc_type, exc_value, exc_traceback):

        if self.file:

            self.file.close()

        if exc_type is not None:

            print('Exception has been handled')

        print('exit')

        return True

with ManagedFile('notes2.txt') as f:

    print('doing stuff...')

    f.write('some todo...')

    f.do_something()

print('continuing...')    

output =                                                

init notes2.txt

enter

doing stuff...

Exception has been handled

exit

continuing...

2.Implementing a context manager as a generator

for example:

from contextlib import contextmanager

@contextmanager

def open_managed_file(filename):

    f = open(filename, 'w')

    try:

        yield f

    finally:

        f.close()

        

with open_managed_file('notes.txt') as f:

    f.write('some todo...')