[issue24969] functools.lru_cache: a way to set decorator arguments at runtime

[Marek Otahal]

New submission from Marek Otahal:

I'd like to use @lru_cache in a library. The problem is I can't know the 
optimal values for 'maxsize', I need to set them at runtime. 

I came with 2 possibilities: 
1/ set cache's size from a hardcoded argument of the decorated method: 
@lru_cache
def foo_long(self, arg1, ..., **kwds):
  pass

# use
foo_long('hi', cacheSize = 1000)

This approach allows the users to customize cache size for their problem. 

2/ from function's **kwds retrieve a name (string) of an instance member of the 
class which will hold the cache's size value. This is not as clean as 1/, but 
offers greated functionality for the use in a library sw: we can compute 
desired cache size from internal values of the unstance, and the use of cache 
can be totally transparent to the end user: 
@lru_cache
def foo_long(self, arg1, .. , **kwds)
#use
foo_long('hi', cacheSizeRef='_cacheSize')

What do you think about the proposal? 
best regards, Mark

--
messages: 249406
nosy: Marek Otahal
priority: normal
severity: normal
status: open
title: functools.lru_cache: a way to set decorator arguments at runtime
type: enhancement

___
Python tracker 
<http://bugs.python.org/issue24969>
___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue24969] functools.lru_cache: a way to set decorator arguments at runtime

[Marek Otahal]

Marek Otahal added the comment:

Hope this example is not too confusing, it's a patch to my code and lru_cache 
(backport for python 2.7 from ActiveState)

It implements both approaches as highlighted above, and in the test both of 
them are used (that does not make much sense, normally one would use either of 
them only)

--

___
Python tracker 
<http://bugs.python.org/issue24969>
___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue24969] functools.lru_cache: a way to set decorator arguments at runtime

[Marek Otahal]

Marek Otahal added the comment:

Hi David, 

> How is (1) different from:
  @lru_cache(maxsize=1000)
   def foo_long(self, arg1...)

As I mentioned, for use in a library that is called by end-users. They can call 
functions and modify params, but do not edit the code. It's up to me (lib devs) 
to prepare the cache decorator. Ie.:
class MyLib():
  @lru_cache
  def foo_long(self, arg1, **kwds):
pass
#user
import MyLib 
i = MyLib()
i.foo_long(1337)

> As for computing it at runtime: if you need to compute it, you can compute it 
> and *then* define the decorator wrapped function.

ditto as above, at runtime no new decorator definitions should be needed for a 
library. 
+ a speed penalty, I'd have to wrap a wrapper in 1 or 2 more nested functions, 
which incures a speed penalty, and we're focusing at cache here. I esp. mention 
this as I've noticed the ongoing effort to use a C implementation of lru_cache 
here.

--

___
Python tracker 
<http://bugs.python.org/issue24969>
___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue24969] functools.lru_cache: a way to set decorator arguments at runtime

[Marek Otahal]

Marek Otahal added the comment:

EDIT: 
> i.foo_long(1337)

ofc, this should be: 
i.foo_long('hi', cacheSize=1337)

or for (2): 

class MyLib():
  def __init__(arg1, arg2):
self._cacheSize = someComputation(arg1, arg2) # returns a number
  @lru_cache
  def foo_long(self, arg1, **kwds):
pass
#user
import MyLib 
i = MyLib(100, 21)
# not to make it so simple: 
i.changeInternalStateSomehow() # updates arg1, arg2, and also _cacheSize
i.foo_long(1337, cacheSizeName='_cacheSize') # ref to self._cacheSize

--

___
Python tracker 
<http://bugs.python.org/issue24969>
___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com