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James Paige
jamesp at westcoastaerospace.com
Tue Jan 24 19:12:45 EST 2006
Wow, thank you Graham! That is a lot of good information. I think the workaround you offered will serve my purposes for now, and I do certainly hope that your proposed changes go into a future version of mod_python. I have a hard time imagining how anyone could possibly argue that the current behavior is non-broken. --- James Paige Graham Dumpleton wrote: > What you are seeing is normal behaviour for mod_python for the way your > code is set up. It is one of a number of cases which highlight the > shortcomings of the module importing and automatic module reloading > system of mod_python. You can read more about some of the problems > with module importing here: > > http://www.dscpl.com.au/articles/modpython-003.html > > More information interspersed below. > > James Paige wrote .. >> I'm new to mod_python... so maybe I have missed something fundamental >> here, but mod_python seems to be keeping several copies of my old code >> in memory, so when I make changes and reload the page, sometimes I get >> my changes, and sometimes I get a seemingly-random version of the code >> that I have already changed. >> >> Here is a simple test-case I set up. >> >> Here is my .htaccess file: >> >> ------------------------- >> SetHandler python-program >> PythonHandler main >> PythonDebug On >> ------------------------- >> >> (I am using version 2.7.10 as shipped in Debian stable's >> libapache-mod-python package, which is why I am using "python-program") >> >> Here is my main.py >> >> ----------------------------- >> from mod_python import apache >> import testmodule >> >> def handler(req): >> req.write("Hello World!") >> testmodule.foo(req) >> return apache.OK >> ----------------------------- >> >> and here is the imported testmodule.py >> >> -------------------------------- >> def foo(req): >> req.write('three blind mice') >> -------------------------------- >> >> The first time I load this test in my web browser, I see the expected >> result: >> >> Hello World!three blind mice >> >> I edit testmodule.py and change the string to something else: >> >> -------------------------------------- >> def foo(req): >> req.write('mary had a little lamb') >> -------------------------------------- >> >> I then reload my web browser. Sometimes this results in "Hello >> World!mary had a little lamb", and sometimes it reuslts in "Hello >> World!three blind mice" > > When you see what you expect, it is because the request was handled by a > different Apache child process which had never previously loaded your > code. Since it is the first time it has needed to load it, it will > obviously get the most recent version. > > When you don't see what you expect, it is because the request was > handled by the the existing Apache child process which had already > loaded the code. > >> I edit the string again, and hit reload again. Maybe I get the new >> string.... or maybe I get one of the strings I used previously. I keep >> making changes to testmodule.py and I keep reloading the results, and >> the results are almost always wrong. >> >> I know this is not a browser cache problem. I have cleared/disabled my >> web-browser's cache. >> >> I read about "Multiple Interpreters" in the documentation, and have >> tried to force my code to run in a single interpreter by adding: >> >> PythonInterpreter "test_interpreter" >> >> to my .htaccess file, but that makes no difference. >> >> This problem only occurs in the included module. I can edit main.py and >> my changes are always applied. I notice in the apache logs that >> everytime I reload the page I see: >> >> [notice] mod_python: (Re)importing main from None > > The automatic module reloading only applies to the top most module, > ie., main.py, and not to anything imported using "import". > >> But I can find no way to force testmodule to be re-imported. What am I >> doing wrong? > > You are not doing anything wrong, the current system simply doesn't > work very well. > > The best you can get is to use: > > from mod_python import apache > import os > > __here__ = os.path.dirname(__file__) > > def handler(req): > req.write("Hello World!") > testmodule = apache.import_module("testmodule,path=[__here__]) > testmodule.foo(req) > return apache.OK > > This uses apache.import_module() on each request to import the module. > In practice though, if the file has not changed it just uses what is already > in the cache. If it has changed, you should then see the change. > > You can't use apache.import_module() at global scope in the module and > get the same effect as that only gets executed when main.py is imported. > Thus you don't get the check for changes to testmodule.py on every > request. > > I have a completely rewritten module importing system for mod_python > which addresses nearly all the issues it has. I will be making it available for > trialing after mod_python 3.2.6 is officially released. It will require though > having 3.2.6, which means it will be useless to you with 2.7.11. > > Whether this new module importing system gets adopted is another > matter entirely though. Some have argued in the past that the current > arrangement is adequate even though it has known problems. ;-( > > Graham >
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