Re: Python 2.6 Global Variables
AK Eric a écrit : 2/ in Python, global really means module-level - there's nothing like a true global namespace. Isn't that __main__? Nope import __main__ __main__.foo = asdfasdf print foo # asdfasdf Not advocating, but it does serve the purpose. This won't make 'foo' available to other imported modules. Still a module-level name, and still no true global namespace - which FWIW is a VeryGoodThing(tm). -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
Bruno Desthuilliers a écrit : AK Eric a écrit : 2/ in Python, global really means module-level - there's nothing like a true global namespace. Isn't that __main__? Nope import __main__ __main__.foo = asdfasdf print foo # asdfasdf Not advocating, but it does serve the purpose. This won't make 'foo' available to other imported modules. Err, reading Steven and Gabriel's posts, it looks like I'm wrong and your right. Duh :( You really shouldn't show this to childrens. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
Gabriel Genellina wrote: div class=moz-text-flowed style=font-family: -moz-fixedEn Fri, 30 Oct 2009 00:29:27 -0300, Steven D'Aprano st...@remove-this-cybersource.com.au escribió: On Thu, 29 Oct 2009 10:31:03 -0700, AK Eric wrote: 2/ in Python, global really means module-level - there's nothing like a true global namespace. snip It isn't a neat trick anymore once you realize the name '__main__' isn't special. Replace __main__ with foo, or config, or whatever, and you get the same results. Ok, there is a catch: a file with that name must exist, at least an empty one... You're just importing the same module from two places; changes done in one place are reflected in the second place, like with any other object. Thanks for saying that. There are two interrelated advantages to using a separate module for the purpose. 1) it avoids circular dependency 2) it makes it clear who gets to initialize these globals; if this module doesn't import anything else (other than stdlib stuff), it'll run to completion before anyone who tries to use these values. So it can give them all their initial value, and avoid anyone else needing to do any existence check nonsense. When I've done it, I've called the module globals.py, or flags.py depending on the primary intent. DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
It isn't a neat trick anymore once you realize the name '__main__' isn't special. Replace __main__ with foo, or config, or whatever, and you get the same results. Ok, there is a catch: a file with that name must exist, at least an empty one... True. I do feel a bit less special now :-P And again, I think there is a difference from saying you *can* work a certain way, and you *should* work a certain way. Making a 'global module' you import and muck with = good. Other ways discussed = bad (for the most part). But I think it's important to understand the underlying system especially when one is first learning: I hand a heck of a time having someone explain this stuff to me when I was learning the basics (and I'm still figuring it out, even from this thread) and now that I get how it works (I uh... think) it makes me a stronger scripter. The common thought seemed to be you shouldn't do it that way, so I'm not going to explain it to you which I've always found quite frustrating. And along those lines... Should we start talking about how you can add stuff to __builtin__ and then it really is exposed to everything? (right, unless I'm missing some other Python idiom?) Again, *not advocating* in standard practice, but I think it's important to understand how it works. (ducks incoming flak) #- # moduleA.py import __builtin__ __builtin__.spam = 42 __builtins__[ham] = 24 #- # moduleB.py # This will fail if moduleA isn't executed first print spam, ham import moduleA import moduleB 42 24 -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
On Fri, Oct 30, 2009 at 9:01 AM, AK Eric warp...@sbcglobal.net wrote: Should we start talking about how you can add stuff to __builtin__ and then it really is exposed to everything? (right, unless I'm missing some other Python idiom?) Again, *not advocating* in standard practice, but I think it's important to understand how it works. (ducks incoming flak) It is important to understand how it works-- but only really in that it's important that people understand how Python handles 'finding' an object when you specify a name... not understanding this leads lots of people to various sorts of confusion, especially as they come from other languages. Python doesn't really have true nested scopes*, it doesn't search up from where you are to go 'higher' and 'higher' and then check some universal-shared global scope, etc. Python has namespaces-- at any given time, there's only three that are accessible. The local namespace, the global namespace, and the builtin namespace. When you reference 'x' in your code, say, as y = x, Python first looks in the local namespace. Failing to find it there, it looks in the global namespace-- which is really the module-level namespace. And, finally, failing that... it looks in the builtin namespace. For, y'know, builtins. * Okay, in Python 2.1/2.2 there was added a limited level of nested scoping to Python for functions embedded in other functions; if a name isn't found in the local scope and the local scope is a nested function, it checks the locals of the containing function too. This is a great addition, but actually seems to have inspired people to think Python has a more pervasive support of dynamic nested scoping going on-- in particular the mythical 'class scope', which it doesn't have. Now, all that said... one should NOT mess around with __builtin__. You may break third-party code you use that way, or at least introduce maintainability nightmares. In Python things don't live off in the ether, everything lives in an explicit place. This is a good thing. Messing with __builtin__ and adding stuff violates this principle. It makes code harder to comprehend by just looking at a single file-- you can't know where everything is defined that way, you can't keep your mind local and 'get' what you're working on. 'from x import *' is a similar problem here, but at least there you have a flag somewhere in the file saying 'hey, go look over here to maybe find that var'. You CAN do it, sure... and there are a some (very, very, very limited!) use-cases where its even good and the right-thing to do, which is why its exposed to you to be ABLE to do it, and doesn't have this giant 'DO NOT DO THIS!' warning in the official docs. But unless you know you must do it to get the result you need-- then the answer to, 'Should I use this feature?' in this case is a resounding no. Use something else instead, even if it doesn't seem as 'nice' to you (such as import settings; settings.blah instead of just blah) IMHO. :) --S -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
In article 888b5e8f-1be5-4040-bc7a-45c2e1695...@d9g2000prh.googlegroups.com, AK Eric warp...@sbcglobal.net wrote: 2/ in Python, global really means module-level - there's nothing like a true global namespace. Isn't that __main__? import __main__ __main__.foo = asdfasdf print foo # asdfasdf Actually, you're almost right, but it's an even WORSE idea than you thought: import __builtin__ __builtin__.foo = 'bar' Kids, do *NOT* do this at home! The reasons why are left as an exercise for the reader. ;-) -- Aahz (a...@pythoncraft.com) * http://www.pythoncraft.com/ You could make Eskimos emigrate to the Sahara by vigorously arguing -- at hundreds of screens' length -- for the wonder, beauty, and utility of snow. --PNH to rb in r.a.sf.f -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
Ronn Ross a écrit : (please don't top-post - fixed) On Oct 28, 2009, at 20:50, mattofak matto...@gmail.com wrote: Hi All; I'm new to Python and moving from C, which is probably a big source of my confusion. I'm struggling with something right now though and I hope you all can help. I have a global configuration that I would like all my classes and modules to be able to access. What is the correct way to do this? Inside the method that you want to use the var prefix the first instance with global. For example: global my_var. Then you can use the var like normal in the method. Good luck Wrong, and wrong again. 1/ you don't have to use the global statement to access a global name - only if you plan on rebinding it (which is more often than not a bad idea but that's another problem) 2/ in Python, global really means module-level - there's nothing like a true global namespace. -- http://mail.python.org/mailman/listinfo/python-list
RE: Python 2.6 Global Variables
Dear all How do I write a code that gets executed 'every x' minutes? I know how to do it 'after x' minutes, I do the following: def doAtTimerFire(): The things I want to do 'after x' minutes go here. And then from main code, I do this: tmr = threading.Timer(timeInSeconds, doAtTimerFire) tmr.start() Please help. Regards, Ashish Vyas -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
On Thu, Oct 29, 2009 at 3:25 AM, VYAS ASHISH M-NTB837 ashish.v...@motorola.com wrote: Dear all How do I write a code that gets executed 'every x' minutes? I know how to do it 'after x' minutes, I do the following: def doAtTimerFire(): The things I want to do 'after x' minutes go here. And then from main code, I do this: tmr = threading.Timer(timeInSeconds, doAtTimerFire) tmr.start() Please help. Regards, Ashish Vyas Please exercise some basic mailinglist etiquette and start a new thread, don't hijack an existing one with a completely unrelated question. New threads are started by emailing your post to python-list@python.org rather than replying to a message on an existing topic. Regards, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
2/ in Python, global really means module-level - there's nothing like a true global namespace. Isn't that __main__? import __main__ __main__.foo = asdfasdf print foo # asdfasdf Not advocating, but it does serve the purpose. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
AK Eric wrote: 2/ in Python, global really means module-level - there's nothing like a true global namespace. Isn't that __main__? import __main__ __main__.foo = asdfasdf print foo # asdfasdf Not advocating, but it does serve the purpose. Good that you're not advocating it, because IMHO it's bad practice to have circular import dependencies. By using the __main__ alias, you avoid the worst problems, but that just means the others are more subtle. You can make it safe, by carefully avoiding certain constructs. But it's still fragile, in that a minor change in one module of the loop can cause either an exception or unexpected behavior. DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
Good that you're not advocating it, because IMHO it's bad practice to have circular import dependencies. By using the __main__ alias, you avoid the worst problems, but that just means the others are more subtle. I figured I'd get that kind of response, not that it's incorrect ;) Great power\great responsibility\etc. As I understand it, when you enter Python statements at the interactive prompt, it's adding the result directly to ___main___ (which for lack of a better term I like to call 'universal' scope... rolls off the tongue better than 'doubleunderscore main doubleunderscore'): foo = 23 import __main__ print __main__.foo 23 While this might not be the most common way of working for most people (I'm guessing most folks are in a nice cozy IDE), people working this way are mucking about in the 'universal' scope without (possibly) even knowing it. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
On Thu, Oct 29, 2009 at 7:11 PM, AK Eric warp...@sbcglobal.net wrote: Good that you're not advocating it, because IMHO it's bad practice to have circular import dependencies. By using the __main__ alias, you avoid the worst problems, but that just means the others are more subtle. I figured I'd get that kind of response, not that it's incorrect ;) Great power\great responsibility\etc. As I understand it, when you enter Python statements at the interactive prompt, it's adding the result directly to ___main___ (which for lack of a better term I like to call 'universal' scope... rolls off the tongue better than 'doubleunderscore main doubleunderscore'): foo = 23 import __main__ print __main__.foo 23 While this might not be the most common way of working for most people (I'm guessing most folks are in a nice cozy IDE), people working this way are mucking about in the 'universal' scope without (possibly) even knowing it. -- Or, you could use any other random module for this like, say, a module made specifically for this purpose and given a name like config.py or settings.py or something like that which describes what you're using it for. You don't have a universal scope- it's the module-level scope of the script that is actually run (or the interactive interpreter in this case). -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
On Thu, 29 Oct 2009 10:31:03 -0700, AK Eric wrote: 2/ in Python, global really means module-level - there's nothing like a true global namespace. Isn't that __main__? Well there you go, I just learned something new. I was going to say No, every module has its own __main__, and say that the only truly global namespace was builtins, which you really shouldn't mess with. But then I decided to just try it, and blow me down, it works! [st...@sylar ~]$ cat set_parrot.py import __main__ __main__.parrot = Norwegian Blue [st...@sylar ~]$ cat get_parrot.py import __main__ print __main__.parrot [st...@sylar ~]$ python Python 2.5 (r25:51908, Nov 6 2007, 16:54:01) [GCC 4.1.2 20070925 (Red Hat 4.1.2-27)] on linux2 Type help, copyright, credits or license for more information. import set_parrot import get_parrot Norwegian Blue I'm sure there are all sorts of odd problems this would lead to in large scale code, but it's a neat trick to know. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
En Fri, 30 Oct 2009 00:29:27 -0300, Steven D'Aprano st...@remove-this-cybersource.com.au escribió: On Thu, 29 Oct 2009 10:31:03 -0700, AK Eric wrote: 2/ in Python, global really means module-level - there's nothing like a true global namespace. Isn't that __main__? Well there you go, I just learned something new. I was going to say No, every module has its own __main__, and say that the only truly global namespace was builtins, which you really shouldn't mess with. But then I decided to just try it, and blow me down, it works! [st...@sylar ~]$ cat set_parrot.py import __main__ __main__.parrot = Norwegian Blue [st...@sylar ~]$ cat get_parrot.py import __main__ print __main__.parrot [st...@sylar ~]$ python Python 2.5 (r25:51908, Nov 6 2007, 16:54:01) [GCC 4.1.2 20070925 (Red Hat 4.1.2-27)] on linux2 Type help, copyright, credits or license for more information. import set_parrot import get_parrot Norwegian Blue I'm sure there are all sorts of odd problems this would lead to in large scale code, but it's a neat trick to know. It isn't a neat trick anymore once you realize the name '__main__' isn't special. Replace __main__ with foo, or config, or whatever, and you get the same results. Ok, there is a catch: a file with that name must exist, at least an empty one... You're just importing the same module from two places; changes done in one place are reflected in the second place, like with any other object. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Python 2.6 Global Variables
Hi All; I'm new to Python and moving from C, which is probably a big source of my confusion. I'm struggling with something right now though and I hope you all can help. I have a global configuration that I would like all my classes and modules to be able to access. What is the correct way to do this? Thanks; Matthew Walker -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
Inside the method that you want to use the var prefix the first instance with global. For example: global my_var. Then you can use the var like normal in the method. Good luck On Oct 28, 2009, at 20:50, mattofak matto...@gmail.com wrote: Hi All; I'm new to Python and moving from C, which is probably a big source of my confusion. I'm struggling with something right now though and I hope you all can help. I have a global configuration that I would like all my classes and modules to be able to access. What is the correct way to do this? Thanks; Matthew Walker -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
On Oct 28, 2009, at 20:50, mattofak matto...@gmail.com wrote: Hi All; I'm new to Python and moving from C, which is probably a big source of my confusion. I'm struggling with something right now though and I hope you all can help. I have a global configuration that I would like all my classes and modules to be able to access. What is the correct way to do this? On Wed, Oct 28, 2009 at 6:02 PM, Ronn Ross ronn.r...@gmail.com wrote: Inside the method that you want to use the var prefix the first instance with global. For example: global my_var. Then you can use the var like normal in the method. Good luck Note that without a global declaration, functions can still read global variables and modify the objects associated with them, but will be unable to re-bind (i.e. reassign) entirely different objects to global variables; the `global` statement just permits them to rebind global variables to new values. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 2.6 Global Variables
On Wed, Oct 28, 2009 at 8:50 PM, mattofak matto...@gmail.com wrote: Hi All; I'm new to Python and moving from C, which is probably a big source of my confusion. I'm struggling with something right now though and I hope you all can help. I have a global configuration that I would like all my classes and modules to be able to access. What is the correct way to do this? Make a separate module with all the config stuff in it, and import that module everywhere you need it. Just make sure you do import settings and not from settings import *. The behavior is different. In the first case, one instance of the module is shared among every module that imports it, so any changes you make will appear in all modules. IN the second case, the current values in settings.py are copied into the local namespace. Changes made in one module won't appear in the other modules. Thanks; Matthew Walker -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
