«

Hi,

I believe I have good understanding of import but it occurred to me that
I might want to remove an imported module. I.e I load a module into ram
and I no longer need the module. Modules just stays in ram? In the
windows world I would "thisform.release()" and the garbage collector
would release the ram. So did I miss something or is there no release
method. How about a method within a class like destroy()?

I just got to believe it's there???? But where?
John

"john fabiani" <> wrote in message
news:4AAnc.6791$ m...
> Hi,
>
> I believe I have good understanding of import but it occurred to me that
> I might want to remove an imported module. I.e I load a module into ram
> and I no longer need the module. Modules just stays in ram? In the
> windows world I would "thisform.release()" and the garbage collector
> would release the ram. So did I miss something or is there no release
> method. How about a method within a class like destroy()?
>
> I just got to believe it's there???? But where?
> John

Well, you were pretty close with calling something like .release(). Use the
del statement.

>>> import random
>>> print random.random()
0.475899061786
>>> del random
>>> print random.random()
Traceback (most recent call last):
File "<stdin>", line 1, in ?
NameError: name 'random' is not defined
>>>

-- Paul

Paul McGuire wrote:

> "john fabiani" <> wrote in message
> news:4AAnc.6791$ m...
>> Hi,
>>
>> I believe I have good understanding of import but it occurred to me that
>> I might want to remove an imported module. I.e I load a module into ram
>> and I no longer need the module. Modules just stays in ram? In the
>> windows world I would "thisform.release()" and the garbage collector
>> would release the ram. So did I miss something or is there no release
>> method. How about a method within a class like destroy()?
>>
>> I just got to believe it's there???? But where?
>> John
>
> Well, you were pretty close with calling something like .release(). Use
> the del statement.
>
>>>> import random
>>>> print random.random()
> 0.475899061786
>>>> del random
>>>> print random.random()
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> NameError: name 'random' is not defined
>>>>

and then

>>> import sys
>>> sys.modules["random"].random()
0.43459738002826365
>>>

should make it clear that (next to) no memory is freed in the process.

Peter

"Peter Otten" <__peter__@web.de> wrote in message
news:c7nvr1$fsc$01$...
> Paul McGuire wrote:
>
> > "john fabiani" <> wrote in message
> > news:4AAnc.6791$ m...
> >> Hi,
> >>
> >> I believe I have good understanding of import but it occurred to me
that
> >> I might want to remove an imported module. I.e I load a module into
ram
> >> and I no longer need the module. Modules just stays in ram? In the
> >> windows world I would "thisform.release()" and the garbage collector
> >> would release the ram. So did I miss something or is there no release
> >> method. How about a method within a class like destroy()?
> >>
> >> I just got to believe it's there???? But where?
> >> John
> >
> > Well, you were pretty close with calling something like .release(). Use
> > the del statement.
> >
> >>>> import random
> >>>> print random.random()
> > 0.475899061786
> >>>> del random
> >>>> print random.random()
> > Traceback (most recent call last):
> > File "<stdin>", line 1, in ?
> > NameError: name 'random' is not defined
> >>>>
>
> and then
>
> >>> import sys
> >>> sys.modules["random"].random()
> 0.43459738002826365
> >>>
>
> should make it clear that (next to) no memory is freed in the process.
>
> Peter
>
So then what if he follows up with:

del sys.modules["random"]

Are there any other dangling references to this module that would stymie the
garbage collector (assuming that the OP hasn't saved off his own reference
to the module)?

-- Paul

Paul McGuire wrote:

> "Peter Otten" <__peter__@web.de> wrote in message
> news:c7nvr1$fsc$01$...
>> Paul McGuire wrote:
>>
>> > "john fabiani" <> wrote in message
>> > news:4AAnc.6791$ m...
>> >> Hi,
>> >>
>> >> I believe I have good understanding of import but it occurred to me
> that
>> >> I might want to remove an imported module. I.e I load a module into
> ram
>> >> and I no longer need the module. Modules just stays in ram? In the
>> >> windows world I would "thisform.release()" and the garbage collector
>> >> would release the ram. So did I miss something or is there no release
>> >> method. How about a method within a class like destroy()?
>> >>
>> >> I just got to believe it's there???? But where?
>> >> John
>> >
>> > Well, you were pretty close with calling something like .release().
>> > Use the del statement.
>> >
>> >>>> import random
>> >>>> print random.random()
>> > 0.475899061786
>> >>>> del random
>> >>>> print random.random()
>> > Traceback (most recent call last):
>> > File "<stdin>", line 1, in ?
>> > NameError: name 'random' is not defined
>> >>>>
>>
>> and then
>>
>> >>> import sys
>> >>> sys.modules["random"].random()
>> 0.43459738002826365
>> >>>
>>
>> should make it clear that (next to) no memory is freed in the process.
>>
>> Peter
>>
> So then what if he follows up with:
>
> del sys.modules["random"]
>
> Are there any other dangling references to this module that would stymie
> the garbage collector (assuming that the OP hasn't saved off his own
> reference to the module)?

Python 2.3.3 (#1, Jan 3 2004, 13:57:0
[GCC 3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import random, sys, weakref
>>> sys.getrefcount(random)
3
>>> del sys.modules["random"]
>>> sys.getrefcount(random)
2

This is one reference for the function call and one for the __main__.random
reference, i. e. reference count should indeed go to zero if we perform

del random

I could not trick the module into telling me directly:

>>> def f(r): print "i'm gone"
....
>>> w = weakref.ref(random, f)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: cannot create weak reference to 'module' object
>>>

Second try, working around the limitations of weak references:

>>> import random, sys, weakref
>>> class Flag: pass
....
>>> random.flag = Flag()
>>> def goodbye(r): print "I'm gone"
....
>>> w = weakref.ref(random.flag, goodbye)
>>> del random
>>> del sys.modules["random"]
I'm gone
>>>

So at least the objects in the module are garbage-collected.

Peter

Paul McGuire wrote:
> "Peter Otten" <__peter__@web.de> wrote in message
> news:c7nvr1$fsc$01$...
>
>>Paul McGuire wrote:
>>
>>
>>>"john fabiani" <> wrote in message
>>>news:4AAnc.6791$ .com...
>>>
>>>>Hi,
>>>>
>>>>I believe I have good understanding of import but it occurred to me
>
> that
>
>>>>I might want to remove an imported module. I.e I load a module into
>
> ram
>
>>>>and I no longer need the module. Modules just stays in ram? In the
>>>>windows world I would "thisform.release()" and the garbage collector
>>>>would release the ram. So did I miss something or is there no release
>>>>method. How about a method within a class like destroy()?
>>>>
>>>>I just got to believe it's there???? But where?
>>>>John
>>>
>>>Well, you were pretty close with calling something like .release(). Use
>>>the del statement.
>>>
>>>
>>>>>>import random
>>>>>>print random.random()
>>>
>>>0.475899061786
>>>
>>>>>>del random
>>>>>>print random.random()
>>>
>>>Traceback (most recent call last):
>>> File "<stdin>", line 1, in ?
>>>NameError: name 'random' is not defined
>>>
>>and then
>>
>>
>>>>>import sys
>>>>>sys.modules["random"].random()
>>
>>0.43459738002826365
>>
>>should make it clear that (next to) no memory is freed in the process.
>>
>>Peter
>>
>
> So then what if he follows up with:
>
> del sys.modules["random"]
>
> Are there any other dangling references to this module that would stymie the
> garbage collector (assuming that the OP hasn't saved off his own reference
> to the module)?
>
> -- Paul
>
>
I think I follow: but doesn't the garbage collector decide what is to
be done? Assuming that there were no dangling references wouldn't the
ram be available for re-use?
John

"john fabiani" <> wrote in message
news:4AAnc.6791$ m...
> Hi,
>
> I believe I have good understanding of import but it occurred to me that
> I might want to remove an imported module. I.e I load a module into ram
> and I no longer need the module. Modules just stays in ram? In the
> windows world I would "thisform.release()" and the garbage collector
> would release the ram. So did I miss something or is there no release
> method. How about a method within a class like destroy()?
>
> I just got to believe it's there???? But where?

The delete statement, in general, directs the interpreter to delete the
association between a name or any other slot and the previously associated
object. Ditto for function locals at function return. It does not tell
the interpreter what to do with a object when its last association
disappears. If, for a particular implementation, it makes sense to talk of
the object being in 'deletable memory' (and, for humans, it hardly does,
nor would it for read-only machine memory, nor, possibly, for 'builtin'
modules), then the standard *allows* but does not *require* deletion.

CPython currently caches a reference to modules so that code like the
following won't tear down a module as it returns and have to rebuild it at
every call:

def sincos(x):
import math as m # for the purpose of this example, assume this is only
math import
return sin(x), cos(x)

Modules are sufficiently small, sufficiently expensive to set up, and
sufficiently often reused, that I has not been thought worthwhile to add a
modwipe function to countervail the cache effect, which itself was added to
countervail the usual CPython delete-object- with-last-reference behavior.

Terry J. Reedy

john fabiani <> writes:

> Paul McGuire wrote:
> > So then what if he follows up with:
> > del sys.modules["random"]
> > Are there any other dangling references to this module that would
> > stymie the
> > garbage collector (assuming that the OP hasn't saved off his own reference
> > to the module)?
> > -- Paul
> >
> I think I follow: but doesn't the garbage collector decide what is to
> be done? Assuming that there were no dangling references wouldn't
> the ram be available for re-use?

Well, that depends on vagaries of your allocator, but probably.

Why are you so worried about the RAM your modules take up?

Cheers,
mwh

--
The use of COBOL cripples the mind; its teaching should, therefore,
be regarded as a criminal offence.
-- Edsger W. Dijkstra, SIGPLAN Notices, Volume 17, Number 5

Michael Hudson wrote:

> john fabiani <> writes:
>
>
>>Paul McGuire wrote:
>>
>>>So then what if he follows up with:
>>> del sys.modules["random"]
>>>Are there any other dangling references to this module that would
>>>stymie the
>>>garbage collector (assuming that the OP hasn't saved off his own reference
>>>to the module)?
>>>-- Paul
>>>
>>
>>I think I follow: but doesn't the garbage collector decide what is to
>>be done? Assuming that there were no dangling references wouldn't
>>the ram be available for re-use?
>
>
> Well, that depends on vagaries of your allocator, but probably.
>
> Why are you so worried about the RAM your modules take up?
>
> Cheers,
> mwh
>
Well I guess I don't have an example that I can bring up. It's just an
after thought that if I create a large program that everything is being
stored in ram (or swap). At some point I'll run out of ram and the more
I limit the stuff I load and can't release the better. In the windows
world I release(). When I monitor the ram usage (task manager) I can
see the ram usage lower when I release(). I keep thinking about all the
forms and the associated code I load in my windows programs. If I kept
all the forms in ram I'd run out quickly. Of course I work with
accounting packages....
John

Terry Reedy wrote:

> "john fabiani" <> wrote in message
> news:4AAnc.6791$ m...
>
>>Hi,
>>
>>I believe I have good understanding of import but it occurred to me that
>>I might want to remove an imported module. I.e I load a module into ram
>>and I no longer need the module. Modules just stays in ram? In the
>>windows world I would "thisform.release()" and the garbage collector
>>would release the ram. So did I miss something or is there no release
>>method. How about a method within a class like destroy()?
>>
>>I just got to believe it's there???? But where?
>
>
> The delete statement, in general, directs the interpreter to delete the
> association between a name or any other slot and the previously associated
> object. Ditto for function locals at function return. It does not tell
> the interpreter what to do with a object when its last association
> disappears. If, for a particular implementation, it makes sense to talk of
> the object being in 'deletable memory' (and, for humans, it hardly does,
> nor would it for read-only machine memory, nor, possibly, for 'builtin'
> modules), then the standard *allows* but does not *require* deletion.
>
> CPython currently caches a reference to modules so that code like the
> following won't tear down a module as it returns and have to rebuild it at
> every call:
>
> def sincos(x):
> import math as m # for the purpose of this example, assume this is only
> math import
> return sin(x), cos(x)
>
> Modules are sufficiently small, sufficiently expensive to set up, and
> sufficiently often reused, that I has not been thought worthwhile to add a
> modwipe function to countervail the cache effect, which itself was added to
> countervail the usual CPython delete-object- with-last-reference behavior.
>
> Terry J. Reedy
>
Note also that there is, AFAICT, no way to reclaim space occupied by the
code of extension modules.

regards
Steve