Commit 36b6c666 authored by Daniel Boeckenhoff's avatar Daniel Boeckenhoff
Browse files

added decorators.py

parent 95b91135
"""
Function decoration
"""
import time
import functools
class cached_property(object):
'''Decorator for read-only properties evaluated only once within TTL period.
It can be used to create a cached property like this::
import random
# the class containing the property must be a new-style class
class MyClass(object):
# create property whose value is cached for ten minutes
@cached_property(ttl=600)
def randint(self):
# will only be evaluated every 10 min. at maximum.
return random.randint(0, 100)
The value is cached in the '_cache' attribute of the object instance that
has the property getter method wrapped by this decorator. The '_cache'
attribute value is a dictionary which has a key for every property of the
object which is wrapped by this decorator. Each entry in the cache is
created only when the property is accessed for the first time and is a
two-element tuple with the last computed property value and the last time
it was updated in seconds since the epoch.
The default time-to-live (TTL) is zero seconds. Set the TTL to
zero for the cached value to never expire.
To expire a cached property value manually just do::
del instance._cache[<property name>]
'''
def __init__(self, ttl=0):
self.ttl = ttl
def __call__(self, fget, doc=None):
self.fget = fget
self.__doc__ = doc or fget.__doc__
self.__name__ = fget.__name__
self.__module__ = fget.__module__
return self
def __get__(self, inst, owner):
now = time.time()
try:
value, last_update = inst._cache[self.__name__]
if self.ttl > 0 and now - last_update > self.ttl:
raise AttributeError
except (KeyError, AttributeError, TypeError):
value = self.fget(inst)
try:
if inst._cache is None:
raise AttributeError
cache = inst._cache
except AttributeError:
cache = inst._cache = {}
cache[self.__name__] = (value, now)
return value
def parametrized(dec):
"""
possibility to parametrize a decorytor
"""
def layer(*args, **kwargs):
def repl(f):
return dec(f, *args, **kwargs)
return repl
return layer
@parametrized
def once(method, arg=False):
"""
Decorator for running a method only once
Examples:
>>> from tfields.lib.decorators import once
>>> class A(object):
... def __init__(self):
... self._once_switch = False
... @property
... def once_switch(self):
... return self._once_switch
... @once_switch.setter
... def once_switch(self, value):
... self._once_switch = value
... @once('once_switch')
... def foo(self):
... return True
>>> a = A()
>>> assert a.once_switch == False
>>> assert a.foo() == True
>>> assert a.once_switch == True
Raises:
>>> assert a.foo() # doctest: +ELLIPSIS
Traceback (most recent call last):
...
RuntimeError: Argument once_switch indicates the method has beenrun already
"""
@functools.wraps(method)
def decorator(self, *args, **kwargs):
if getattr(self, arg):
raise RuntimeError("Argument {arg} indicates the method has been"
"run already".format(**locals()))
value = method(self, *args, **kwargs)
setattr(self, arg, True)
return value
return decorator
if __name__ == '__main__':
import doctest
doctest.testmod()
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