There are some resources we need to release when we finish our job. It is easy for us to forget
those operations. Python has a keyword with which can be used to help solve this problem.
After we go out the scope of with, python will make sure certain operations will be executed.
- Introduction
- contextlib.contextmanager
- contextlib.closing
- contextlib.ContextDecorator
- contextlib.suppress(*excpetions)
- contextlib.redirect_stdout/redirect_stderr
Introduction
Python’s module contextlib provides some common utilities to help write code which needs to
execute operations when leaving the scope.
contextlib.contextmanager
This decorator makes any function which uses the yield keyword work with with clause.
from contextlib import contextmanager
@contextmanager
def say_hi():
print("HI")
a = 3
yield a
print("Hello")
with say_hi() as a:
print(a)
The statements before yield will be executed before entering with, the statements after
will be executed when leaving out the scope.
contextlib.closing
Works with object which implements a close() function such as a socket connection.
from contextlib import closing
class Close(object):
def say_hi(self):
print("say hi")
def close(self):
print("closing")
with closing(CLose()) as close:
close.say_hi()
contextlib.ContextDecorator
It makes the instance as a contextmanager.
from contextlib import ContextDecorator
class Manager(ContextDecorator):
def __enter__(self):
print("Entering")
def __exit__(self, *exc):
print("Exiting")
@Manager()
def fun():
pass
contextlib.suppress(*excpetions)
Used to suppress exception. It is useful and can be used to replace the try/catch clauses.
from contextlib import suppress, nullcontext
def fun():
raise Exception("xx")
with suppress(Exception):
func()
with nullcontext():
func()
contextlib.redirect_stdout/redirect_stderr
Redirect to other file handlers.
from contextlib import redirect_stdout
def fun():
print("HI")
with open("log", "w") as fd:
with redirect_stdout(fd):
func()