python的闭包和装饰器
closure
https://www.programiz.com/python-programming/closure
def get_config_table():
cfg = {
'a':1, 'b':2}
return cfg
def get_config_index():
config_table = get_config_table()
def wrapper(cfg_name):
return config_table.get(cfg_name, 'NULL')
return wrapper
f=get_config_index()
f('a')
1
decorator
decorator pattern
Simple demo
from datetime import datetime
from functools import wraps
def time_this(func):
#@wraps(func)
def wrapper(*args, **kwargs):
begin = datetime.now()
res = func(*args, **kwargs)
end = datetime.now()
print("{} costs:{}".format(func.__name__, end - begin))
return res
return wrapper
@time_this
def count(num):
import time
time.sleep(num)
def count1(num):
import time
time.sleep(num)
count1 = time_this(count1)
count(2)
count1(2)
class Foo:
@time_this
def _sub(self, n):
print("_sub")
@time_this
def foo1(self, num):
self._sub(9)
print("Foo.foo1")
f = Foo()
f.foo1(2)
count costs:0:00:02.000687
count1 costs:0:00:02.000561
_sub
_sub costs:0:00:00.000988
Foo.foo1
foo1 costs:0:00:00.000988
Discussion
-
decorating happens durning import
-
understand it by count = time_this(count), syntactic suger make it easy to use but far to understand
-
cellphone case
-
make a cellphone
-
make cellphone wrapper
-
wrap—>return a closure which stores the function
-
a case of closure
With parameter
Define
from functools import wraps
def requires_permission(sPermission):
def decorator(fn):
@wraps(fn)
def decorated(*args,**kwargs):
print("by function decorator")
lPermissions = get_permissions(current_user_id())
if sPermission in lPermissions:
return fn(*args,**kwargs)
raise Exception("You need '{}' permission".format(sPermission))
return decorated
return decorator
def get_permissions(iUserId):
return {
1: ('logged_in', 'premium_member')}[iUserId]
@requires_permission('administrator')
def delete_user(iUserId):
pass
@requires_permission('logged_in')
def new_game():
pass
@requires_permission('premium_member')
def premium_checkpoint():
pass
def current_user_id():
return 1
Test
def test():
from functools import partial
for fun in (partial(delete_user, 1), new_game, premium_checkpoint):
try:
fun()
except Exception as e:
print("test {} with error '{}'".format(fun, str(e)))
else:
print("test {} OK".format(fun))
test()
test functools.partial(.wrapper at 0x00000215357198B8>, 1) with error 'permission denied'
test <__main__.require_permission_by_class object at 0x0000021534BA32C8> OK
test <__main__.require_permission_by_class object at 0x0000021534BA3FC8> OK
Decorator as class
class require_permission_by_class(object):
def __init__(self, permission, func):
self._func = func
self._permission = permission
def __call__(self, *args, **kwargs):
print("by class for {}".format(self._func.__name__))
lPermissions = get_permissions(current_user_id())
if self._permission in lPermissions:
return self._func(*args,**kwargs)
raise Exception("permission denied")
def get_permissions(iUserId):
return {
1: ('logged_in', 'premium_member')}[iUserId]
def delete_user(iUserId):
pass
delete_user=require_permission_by_class('administrator', delete_user)
def new_game():
pass
new_game=require_permission_by_class('logged_in', new_game)
dec1=lambda f:require_permission_by_class('premium_member', f)
@dec1
def premium_checkpoint():
pass
#premium_checkpoint=require_permission_by_class('premium_member', premium_checkpoint)
def current_user_id():
return 1
def test():
from functools import partial
for fun in (partial(delete_user, 1), new_game, premium_checkpoint):
try:
fun()
except Exception as e:
print("test {} with error '{}'".format(fun, str(e)))
else:
print("test {} OK".format(fun))
test()
by class for delete_user
test functools.partial(<__main__.require_permission_by_class object at 0x0000021534C20348>, 1) with error 'permission denied'
by class for new_game
test <__main__.require_permission_by_class object at 0x0000021535441948> OK
by class for premium_checkpoint
test <__main__.require_permission_by_class object at 0x0000021534D18C08> OK
Another way
class require_permission_by_class_v1(object):
def __init__(self, permission):
self._permission = permission
def __call__(self, func, *args, **kwargs):
def wrapper(*args, **kwargs):
print("by class v1 for {}".format(func.__name__))
lPermissions = get_permissions(current_user_id())
if self._permission in lPermissions:
return self._func(*args,**kwargs)
raise Exception("permission denied")
return wrapper
@require_permission_by_class_v1('administrator')
def delete_user(iUserId):
pass
#delete_user=require_permission_by_class_v1('administrator')(delete_user)
Test
test()
by class v1 for delete_user
test functools.partial(.wrapper at 0x0000021534F9FCA8>, 1) with error 'permission denied'
by class for new_game
test <__main__.require_permission_by_class object at 0x0000021535441948> OK
by class for premium_checkpoint
test <__main__.require_permission_by_class object at 0x0000021534D18C08> OK
decorate multiple times
def retry(nums):
def decorator(fun):
def wrapper(*args, **kwargs):
for i in range(nums):
try:
return fun(*args, **kwargs)
except Exception as e:
print("{} fail{}".format(fun.__name__, ' retry...' if i < nums -1 else ''))
return wrapper
return decorator
@time_this
@retry(3)
def must_be_fail():
raise Exception("bad guy")
must_be_fail()
Summary
- Add aditional function before and after function
- Know the classic usage cases to give you enlightenment:
- log
- time cost
- exception handle
- permission manager
- retry
- …