13 Python Context Manager

python context manager

use contextlib/yield

@contextmanager
def send_mail_context():
    '''context manager

    with send_mail_context()
    '''
    try:
        # 1 doing work BEFORE the code goes into with block
        print('before yield')
        server = smtplib.SMTP(SMTP_SERVERS[0], 25)
        # 2 yield back to with/caller
        yield server
    except Exception as e:
        print(e)
    finally:
        # 4. doing cleanup work
        server.quit()
        print('in finally')

use class __enter__, __exit__

# 2 implement contextmanager with class
class SMTPCT(object):
    '''

    1. override __enter__ __exit__
    2. in __enter__, return value
    '''
    def __init__(self):
        self.smtp_server = None

    def __enter__(self):
        # 1 doing work BEFORE the code goes into with block
        print('in enter')
        self.smtp_server = smtplib.SMTP(SMTP_SERVERS[0], 25)
        # 2 return back to with/caller
        return self.smtp_server

    def __exit__(self, type, value, traceback):
        # 4. doing cleanup work
        print('in exit')
        self.smtp_server.quit()