Re-hi and thank you. That solved my problem. I can now see that the base_plugin.Plugin is loaded several times. The numeric id(the_class) is not the same in all places.
Anyway, I thought that a class is always the same if it has been loaded from the same module (in Linux/Unix; from the same file and inode). So this experience was a bit confusing. I need to learn more about how to set the search path (sys.path) right. More Python! Thanks Osmo Antero Grønland, Oslo On 08/29/2010 01:06 PM, Peter Otten wrote: > Osmo Maatta wrote: > >> Hello, >> >> Sub class test fails. >> ====================== >> I have a program that needs to load plugin-classes during runtime. >> >> The program has these subdirectories (modules). >> >> $ tree >> . >> `-- test.py >> | >> |-- plugins >> | |-- base_plugin.py >> | |-- base_plugin.pyc >> | |-- __init__.py >> | `-- oca >> | |-- __init__.py >> | |-- open_clipart.py >> >> >> The plugins (sub directory) contains one or more plugin modules, in this >> test-case there is only one; oca/open_clipart.py. >> >> The plugins/base_plugin.py (contains class Plugin()) is a base class of >> all plugins. >> >> I want to list and load all plugin-classes (that inherit from >> base_plugin.Plugin). I have a Python code that successfully browses the >> plugins, but the the test issubclass(x, base_plugin.Plugin) fails. >> >> Please see this Python code: >> http://futuredesktop.com/tmp/test6.tar.gz >> >> Why the issubclass(entry, cls) test fails? > > base_plugin.py is imported twice, once as plugins.base_plugin and a second > time as base_plugin. You can see that when you add a bit more debug code > into your test.py: > > > --- a/test.py Sun Aug 29 12:57:25 2010 +0200 > +++ b/test.py Sun Aug 29 12:58:25 2010 +0200 > @@ -24,6 +24,8 @@ > #print "entry's class<%s> -- cls's class=<%s>" % > (obj1.get_name(), obj2.get_name(), ) > > print "Check %s against %s" % (entry, cls, ) > + print entry.__bases__ > + print cls > > if issubclass(entry, cls): > print "Found a subclass: " + key > > $ python test.py > Importing plugins.base_plugin > Importing plugins.oca.open_clipart > Check <class 'plugins.oca.open_clipart.OpenClipArt'> against <class > 'plugins.base_plugin.Plugin'> > (<class 'base_plugin.Plugin'>,) > <class 'plugins.base_plugin.Plugin'> > Got subclasses= [] > > The solution is to remove all sys.path gymnastics and to adapt your import > statements accordingly: > > $ hg diff > diff -r 9fe6129ba8fc plugins/oca/open_clipart.py > --- a/plugins/oca/open_clipart.py Sun Aug 29 12:51:51 2010 +0200 > +++ b/plugins/oca/open_clipart.py Sun Aug 29 13:02:55 2010 +0200 > @@ -2,9 +2,7 @@ > import os > import threading, thread > > -sys.path.insert(0, '..') > -import base_plugin > -#sys.path.insert(0, '../..') > +from .. import base_plugin > > # ------------------------------------------ > # class OpenClipArt > diff -r 9fe6129ba8fc test.py > --- a/test.py Sun Aug 29 12:51:51 2010 +0200 > +++ b/test.py Sun Aug 29 13:02:55 2010 +0200 > @@ -1,7 +1,6 @@ > import os, sys > import inspect > > -sys.path.insert(0, "plugins") > > # Thanks to http://www.luckydonkey.com/2008/01/02/python-style-plugins- > made-easy/ > def find_subclasses(path, cls): > > > $ python test.py > Importing plugins.base_plugin > Importing plugins.oca.open_clipart > Check <class 'plugins.oca.open_clipart.OpenClipArt'> against <class > 'plugins.base_plugin.Plugin'> > Found a subclass: OpenClipArt > Got subclasses= [<class 'plugins.oca.open_clipart.OpenClipArt'>] > > You should also remove the __init__.py from the folder containing test.py > which is just begging for the same problem when you import your plugins as > test.plugins.whatever. > > Peter > -- http://mail.python.org/mailman/listinfo/python-list
