472,993 Members | 2,638 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 472,993 software developers and data experts.

Consequences of importing the same module multiple times in C++?

Hi,

I'm currently using boost::python::import() to import Python modules,
so I'm not sure exactly which Python API function it is calling to
import these files. I posted to the Boost.Python mailing list with
this question and they said I'd probably get a better answer here, so
here it goes...

If I do the following:

using namespace boost::python;
import( "__main__" ).attr( "new_global" ) = 40.0f;
import( "__main__" ).attr( "another_global" ) = 100.0f:

Notice that I'm importing twice. What would be the performance
consequences of this? Do both import operations query the disk for the
module and load it into memory? Will the second call simply reference
a cached version of the module loaded at the first import() call?

Thanks.
Oct 24 '08 #1
2 2172
On Fri, 24 Oct 2008 12:23:18 -0700, Robert Dailey wrote:
Hi,

I'm currently using boost::python::import() to import Python modules, so
I'm not sure exactly which Python API function it is calling to import
these files. I posted to the Boost.Python mailing list with this
question and they said I'd probably get a better answer here, so here it
goes...

If I do the following:

using namespace boost::python;
import( "__main__" ).attr( "new_global" ) = 40.0f; import( "__main__"
).attr( "another_global" ) = 100.0f:

Notice that I'm importing twice. What would be the performance
consequences of this? Do both import operations query the disk for the
module and load it into memory? Will the second call simply reference a
cached version of the module loaded at the first import() call?

Thanks.
I think it does not reload the module. Running python with verbose mode:

blah@blah-laptop:~$ python -v
(snip)
>>import xml
import xml # directory /usr/local/lib/python2.6/xml
# /usr/local/lib/python2.6/xml/__init__.pyc matches /usr/local/lib/
python2.6/xml/__init__.py
import xml # precompiled from /usr/local/lib/python2.6/xml/__init__.pyc
>>import xml
It's also mentioned in the docs: (paraphrased to clarify the points)
'''
The system maintains a table of modules that have been ...
initialized.... When a module name is found..., step (1) is finished. If
not, a search for a module ... . When ... found, it is loaded.
'''
http://www.python.org/doc/2.5.2/ref/import.html

Oct 25 '08 #2
On Oct 24, 2:23*pm, Robert Dailey <rcdai...@gmail.comwrote:
Hi,

I'm currently using boost::python::import() to import Python modules,
so I'm not sure exactly which Python API function it is calling to
import these files. I posted to the Boost.Python mailing list with
this question and they said I'd probably get a better answer here, so
here it goes...

If I do the following:

using namespace boost::python;
import( "__main__" ).attr( "new_global" ) = 40.0f;
import( "__main__" ).attr( "another_global" ) = 100.0f:

Notice that I'm importing twice. What would be the performance
consequences of this? Do both import operations query the disk for the
module and load it into memory? Will the second call simply reference
a cached version of the module loaded at the first import() call?

Thanks.
Docs:

Note
For efficiency reasons, each module is only imported once per
interpreter session. Therefore, if you change your modules, you must
restart the interpreter or, if its just one module you want to test
interactively, use reload(), e.g. reload(modulename).

Oct 25 '08 #3

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

0
by: OKB (not okblacke) | last post by:
I'm fooling around with some MUD server code, and I want to add a "reload" command that will let MUD wizards reload the server modules, so that changes to the MUD parser and such can be effected...
4
by: Active8 | last post by:
I did this once and can't remember how <blush> so I read the reportlab user guid. It says to unzip the reportlab archive - this is on w2k, BTW, with Python23 - to a directory and make a file...
12
by: qwweeeit | last post by:
The pythonic way of programming requires, as far as I know, to spread a big application in plenty of more manageable scripts, using import or from ... import to connect the various modules. In...
4
by: Brian K. | last post by:
I am trying to split up and secure a database that we've been using on a network for a few years, following the procedure listed in Q304932 from microsoft. I create a new blank database for...
14
by: T. Crane | last post by:
Hi, When troubleshooting code that's saved in a text file, I often find that I want to make a change to it, re-save it, then reimport it. However, just typing import myTestCode doesn't...
9
by: rbygscrsepda | last post by:
Hi, I'm a newbie at Python. :) Right now it's not letting me import * from any relative package name--i.e., a name that starts with a dot. For instance, none of the following work: from . import...
4
by: rkmr.em | last post by:
Hi I have a function data, that I need to import from a file data, in the directory data If I do this from python interactive shell (linux fedora core 8) from dir /home/mark it works fine: ...
7
by: Hussein B | last post by:
Hey, Suppose I have a Python application consists of many modules (lets say it is a Django application). If all the modules files are importing sys module, how many times the sys module will be...
0
by: lllomh | last post by:
Define the method first this.state = { buttonBackgroundColor: 'green', isBlinking: false, // A new status is added to identify whether the button is blinking or not } autoStart=()=>{
2
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 4 Oct 2023 starting at 18:00 UK time (6PM UTC+1) and finishing at about 19:15 (7.15PM) The start time is equivalent to 19:00 (7PM) in Central...
0
by: Aliciasmith | last post by:
In an age dominated by smartphones, having a mobile app for your business is no longer an option; it's a necessity. Whether you're a startup or an established enterprise, finding the right mobile app...
2
by: giovanniandrean | last post by:
The energy model is structured as follows and uses excel sheets to give input data: 1-Utility.py contains all the functions needed to calculate the variables and other minor things (mentions...
4
NeoPa
by: NeoPa | last post by:
Hello everyone. I find myself stuck trying to find the VBA way to get Access to create a PDF of the currently-selected (and open) object (Form or Report). I know it can be done by selecting :...
3
NeoPa
by: NeoPa | last post by:
Introduction For this article I'll be using a very simple database which has Form (clsForm) & Report (clsReport) classes that simply handle making the calling Form invisible until the Form, or all...
3
by: nia12 | last post by:
Hi there, I am very new to Access so apologies if any of this is obvious/not clear. I am creating a data collection tool for health care employees to complete. It consists of a number of...
0
NeoPa
by: NeoPa | last post by:
Introduction For this article I'll be focusing on the Report (clsReport) class. This simply handles making the calling Form invisible until all of the Reports opened by it have been closed, when it...
3
SueHopson
by: SueHopson | last post by:
Hi All, I'm trying to create a single code (run off a button that calls the Private Sub) for our parts list report that will allow the user to filter by either/both PartVendor and PartType. On...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.