Re: Problem with reimporting modules
Thanks for the detailed explanations, Gabriel. > At that time, all values in the module namespace are set to > None (for breaking possible cycles, I presume). print_hello now has a > func_globals with all names set to None. (Perhaps the names could have > been deleted instead, so print_hello() would raise a NameError, but I'm > just describing the current CPython implementation) Yes, that was the thing that confused me a bit. I had expected that an error is raised or that the namespace has a reference to the module and is reestablished when the module has been reloaded. Anyway, I have solved the problem in a different way now. -- Christoph -- http://mail.python.org/mailman/listinfo/python-list
Re: Problem with reimporting modules
En Sun, 11 Feb 2007 15:56:16 -0300, Christoph Zwerschke <[EMAIL PROTECTED]> escribió: > Yes I know about reload(), but TurboGears (TurboKid) does not use it and > the docs say that removing modules from sys.module is possible to force > reloading of modules. I don't want to rewrite everything since it's a > pretty complex thing with modules which are compiled from templates > which can depend from other templates etc... If you remove the module from sys.modules, when you import it again you end up with a *new*, fresh, module object, unrelated to the original one. Quoting your original message again: > I tracked it down to the following behavior of Python. Assume you have a > module hello.py like that: > hello. py > greeting = 'Hello!' > def print_hello(): > print greeting > --- > Now run the following code: > from hello import print_hello > print_hello() > import sys > del sys.modules['hello'] # delete module > import hello # recreate module > print_hello() > The second print_hello() prints "None" instead of "Hello!". Why is that? Notice that you are mixing references here. You first import print_hello from hello, and after deleting the module, you import hello (not print_hello). And you expect that your old reference to print_hello now refers to the new function. The whole point of reloading/reimporting a module is to get the *new* contents, but that only works if you refer to things using the module.function notation, not if you hold a reference to the function (which will always be the original function). In short, your code should be: import hello hello.print_hello() import sys del sys.modules['hello'] import hello hello.print_hello() or, using reload: import hello hello.print_hello() reload(hello) hello.print_hello() If you think that always typing module.function is too much - well, don't try to reload modules then :) Somewhere I read that at Google the policy is to always import modules, never functions, and this may be a good reason for it. If you want to know the details: print_hello doesn't hold a reference to the containing module, only to its namespace, in the func_globals attribute. When you delete the last reference to the module, it gets destroyed. At that time, all values in the module namespace are set to None (for breaking possible cycles, I presume). print_hello now has a func_globals with all names set to None. (Perhaps the names could have been deleted instead, so print_hello() would raise a NameError, but I'm just describing the current CPython implementation) -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: Problem with reimporting modules
Yes I know about reload(), but TurboGears (TurboKid) does not use it and the docs say that removing modules from sys.module is possible to force reloading of modules. I don't want to rewrite everything since it's a pretty complex thing with modules which are compiled from templates which can depend from other templates etc... -- http://mail.python.org/mailman/listinfo/python-list
Re: Problem with reimporting modules
On Feb 11, 5:53 am, Christoph Zwerschke <[EMAIL PROTECTED]> wrote: > I'm currently investigating a problem that can hit you in TurboGears > when Kid template modules are reloaded in the background, because in > certain situations, global variables suddenly are set to None values. > > I tracked it down to the following behavior of Python. Assume you have a > module hello.py like that: > > hello. py > greeting = 'Hello!' > def print_hello(): > print greeting > --- > > Now run the following code: > > from hello import print_hello > print_hello() > import sys > del sys.modules['hello'] # delete module > import hello # recreate module > print_hello() > > The second print_hello() prints "None" instead of "Hello!". Why is that? > I had expected that it either prints an error or print "Hello!" as well. > > Is this intended behavior of Python? > > -- Christoph You're most likely looking for reload: http://docs.python.org/lib/built-in-funcs.html#l2h-61 The documentation does imply that deleting a module from sys.modules may not be what you want: http://docs.python.org/lib/module-sys.html#l2h-5147 >>> import sys >>> import warnings as previous_warnings # for example >>> # testing whether reload returns the same module object: ... reload(previous_warnings) is previous_warnings True >>> # the following result is rather intuitive, but for ... # the sake of demonstration, I'll do it anyway. ... del sys.modules['warnings'] >>> import warnings as after_warnings >>> after_warnings is previous_warnings False -- http://mail.python.org/mailman/listinfo/python-list
