Re: unexpected behavior: did i create a pointer?
neoedmund a écrit : On Sep 7, 4:07 pm, gu [EMAIL PROTECTED] wrote: (snip pb and code) now, in the second for cycle and in functionA() i only 'touch' copyOfA (altering it). as i don't touch the variable a, i expect it not to be affected by any change, but copyOfA acts like a pointer to a and altering copyOfA's values result in altering the values of a, so the result that i expect is: (snip) no language act like want you tought, or the assignment operation will be too expensive. IIRC, php4 was doing copies for arrays... -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
En Wed, 12 Sep 2007 08:30:14 -0300, Bruno Desthuilliers [EMAIL PROTECTED] escribi�: neoedmund a écrit : On Sep 7, 4:07 pm, gu [EMAIL PROTECTED] wrote: (snip pb and code) now, in the second for cycle and in functionA() i only 'touch' copyOfA (altering it). as i don't touch the variable a, i expect it not to be affected by any change, but copyOfA acts like a pointer to a and altering copyOfA's values result in altering the values of a, so the result that i expect is: (snip) no language act like want you tought, or the assignment operation will be too expensive. IIRC, php4 was doing copies for arrays... Pascal does copy arrays and structs (records) too. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Am Sat, 08 Sep 2007 09:44:24 + schrieb Steven D'Aprano: Ways that Python objects are not like C pointers: (1) You don't have to manage memory yourself. (2) You don't have typecasts. You can't change the type of the object you point to. (3) Python makes no promises about the memory location of objects. (4) No pointer arithmetic. (5) No pointers to pointers, and for old-school Mac programmers, no handles. (6) No dangling pointers. Ever. (7) There's no null pointer. None is an object, just like everything else. (8) You can't crash your computer by writing the wrong thing to the wrong pointer. You're unlikely even to crash your Python session. Ways that Python objects are like pointers: (1) ... um... Oh yeah, if you bind the _same_ object to two different names, _and_ the object is mutable (but not if it is immutable), mutating the object via one name will have the same effect on the object -- the same object, naturally -- bound to the other name. Had you put it that way in the first place I would have stayed in in my hole ;) Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Sep 7, 4:07 pm, gu [EMAIL PROTECTED] wrote: hi to all! after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: code a = {} for x in range(10): for y in range(10): a[x,y] = 0 copyOfA = a def functionA(x,y): print a[x,y], copyOfA[x,y] = * print a[x,y],copyOfA[x,y] for x in range(10): for y in range(10): functionA(x,y) /code now, in the second for cycle and in functionA() i only 'touch' copyOfA (altering it). as i don't touch the variable a, i expect it not to be affected by any change, but copyOfA acts like a pointer to a and altering copyOfA's values result in altering the values of a, so the result that i expect is: 0 0 * 0 0 * 0 0 * 0 0 * [..] but i get: 0 * * 0 * * 0 * * 0 * * [..] what's going on? thanks in advance. no language act like want you tought, or the assignment operation will be too expensive. -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Sep 8, 10:44 am, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: [...] Ways that Python objects are like pointers: (1) ... um... Oh yeah, if you bind the _same_ object to two different names, _and_ the object is mutable (but not if it is immutable), mutating the object via one name will have the same effect on the object -- the same object, naturally -- bound to the other name. Well one of the main uses of pointers in C is as things that *point to* objects. And AFAIK that's exactly what a name is in Python. In fact I think to say that a name points to (or refers to) an object is less misleading that to say it is bound to. Binding implies some sort of symmetry but when I write: a = Am I bound? The name a knows it's refering to the string object, whereas the string has no idea who refers to it (well an implementation might want to store this information, but it is inaccessible). You know, maybe because I came to Python with no C experience, I never had trouble with the unexpected behaviour that so confused the original poster. It's just obvious. The funny thing is that if the OP had thought of both 'a' and 'copyOfA' as C-like pointers then he wouldn't have been confused :) -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Sun, 09 Sep 2007 02:30:00 -0700, Arnaud Delobelle wrote: You know, maybe because I came to Python with no C experience, I never had trouble with the unexpected behaviour that so confused the original poster. It's just obvious. The funny thing is that if the OP had thought of both 'a' and 'copyOfA' as C-like pointers then he wouldn't have been confused :) You're almost certainly wrong. He would have written to ask why this doesn't do what he expects: x = 3 y = x # x and y are both pointers to the same value x += 1 print x == y # of course, they are pointers to the same value False Or why lower_list() works as expected, but lower_string() doesn't: def lower_list(L): ... for i, x in enumerate(L): ... L[i] = x.lower() ... s = ['STRING'] lower_list(s) print s == ['string'] True def lower_string(s): ... s = s.lower() ... s = STRING lower_string(s) print s == string False The names in Python are pointers analogy only gives you the right answer half the time. The names in Python are names analogy gives you the right answer ALL THE TIME, no exceptions. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Sep 9, 1:59 pm, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: On Sun, 09 Sep 2007 02:30:00 -0700, Arnaud Delobelle wrote: You know, maybe because I came to Python with no C experience, I never had trouble with the unexpected behaviour that so confused the original poster. It's just obvious. The funny thing is that if the OP had thought of both 'a' and 'copyOfA' as C-like pointers then he wouldn't have been confused :) You're almost certainly wrong. He would have written to ask why this doesn't do what he expects: x = 3 y = x # x and y are both pointers to the same value x += 1 This means that x now points to the value of x + 1, i.e. an int object with value 4. print x == y # of course, they are pointers to the same value Of course not, now x points to 4 and y points to 3 ! False Or why lower_list() works as expected, but lower_string() doesn't: def lower_list(L): ... for i, x in enumerate(L): ... L[i] = x.lower() ... s = ['STRING'] lower_list(s) print s == ['string'] True def lower_string(s): ... s = s.lower() ... s = STRING lower_string(s) Let's see what happens here: when lower_string(s) is called, the 's' which is local to lower_string is made to point to the same object as the global s (i.e. the string object with value STRING). In the body of the function, the statement s=s.lower() makes the local 's' point to a new string object returned s.lower(). Of course this has not effect on what object the global 's' points to. print s == string Obviously not, since s still points to the string object with value STRING False The names in Python are pointers analogy only gives you the right answer half the time. They give *you* the right answer only half the time ;) They give me the right answer all the time. Not that I usually think of names as pointers. But if I choose to do so, I can still get it right. And if it works for me consistently, there must be some validity in it, no? What I think is a more dangerous misconception is to think that the assignement operator (=) has the same meaning in C and python. -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Arnaud Delobelle [EMAIL PROTECTED] wrote: ... def lower_list(L): ... for i, x in enumerate(L): ... L[i] = x.lower() ... s = ['STRING'] lower_list(s) print s == ['string'] True def lower_string(s): ... s = s.lower() ... s = STRING lower_string(s) Let's see what happens here: when lower_string(s) is called, the 's' which is local to lower_string is made to point to the same object as the global s (i.e. the string object with value STRING). In the body of the function, the statement s=s.lower() makes the local 's' point to a new string object returned s.lower(). Of course this has not effect on what object the global 's' points to. Yep, the analogy with C pointers would work fine here: void lower_string(char* s) { s = whatever } would fail to have the intended effect in C just as its equivalent does in Python (in both Python and C, rebinding the local name s has no effect on the caller of lower_string). Add an indirection: void lower_list(item* L) { ... L[i] = something } this indirection (via indexing) *does* modify the memory area (visible by the caller) to which L points. The difference between name=something and name[i]=something is so *HUGE* in C (and in Python) that anybody who doesn't grok that difference just doesn't know or understand any C (nor any Python). What I think is a more dangerous misconception is to think that the assignement operator (=) has the same meaning in C and python. I've seen the prevalence of that particular misconception drop dramatically over the years, as a growing fraction of the people who come to Python after some previous programming experience become more and more likely to have been exposed to *Java*, where assignment semantics are very close to Python (despite Java's unfortunate complication with unboxed elementary scalar types, in practice a vast majority of occurrences of a=b in Java have just the same semantics as they do in Python); teaching Python semantics to people with Java exposure is trivially easy (moving from ALMOST every variable is an implicit reference -- excepting int and float ones to EVERY variable is an implicit reference...). Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Am Sat, 08 Sep 2007 00:32:35 + schrieb Steven D'Aprano: On Fri, 07 Sep 2007 15:59:53 +0200, Wildemar Wildenburger wrote: I just thought I'd go along with the analogy the OP created as that was his mindset and it would make things easier to follow if I didn't try to forcibly change that. My reaction to somebody trying to reason with the wrong analogy is to teach them the right analogy, not to tell them they got it right when they actually got it wrong. My car won't start -- I must not have stirred the gasoline enough before baking it. Yes, that's right. It's very important to stir the gasoline fully so that all the ingredients are fully mixed. I think Wildemar is too defensive. The pointer analogy is a good first approximation, not cargo cult. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Am Fri, 07 Sep 2007 13:10:16 + schrieb Grant Edwards: On 2007-09-07, Peter Otten [EMAIL PROTECTED] wrote: Am Fri, 07 Sep 2007 10:40:47 + schrieb Steven D'Aprano: Python doesn't have any pointers. Thinking of python variables or names as pointers should get you a long way when trying to understand python's behaviour. But thinking of them as names bound to objects will get you further (and get you there faster). ;) Understanding a new system in terms of one I already know works for me. When terminology and the system it describes make a perfect fit that is a strong indication that you have reached a dead end. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Sat, 08 Sep 2007 10:07:14 +0200, Peter Otten wrote: Am Fri, 07 Sep 2007 13:10:16 + schrieb Grant Edwards: On 2007-09-07, Peter Otten [EMAIL PROTECTED] wrote: Am Fri, 07 Sep 2007 10:40:47 + schrieb Steven D'Aprano: Python doesn't have any pointers. Thinking of python variables or names as pointers should get you a long way when trying to understand python's behaviour. But thinking of them as names bound to objects will get you further (and get you there faster). ;) Understanding a new system in terms of one I already know works for me. When terminology and the system it describes make a perfect fit that is a strong indication that you have reached a dead end. Ways that Python objects are not like C pointers: (1) You don't have to manage memory yourself. (2) You don't have typecasts. You can't change the type of the object you point to. (3) Python makes no promises about the memory location of objects. (4) No pointer arithmetic. (5) No pointers to pointers, and for old-school Mac programmers, no handles. (6) No dangling pointers. Ever. (7) There's no null pointer. None is an object, just like everything else. (8) You can't crash your computer by writing the wrong thing to the wrong pointer. You're unlikely even to crash your Python session. Ways that Python objects are like pointers: (1) ... um... Oh yeah, if you bind the _same_ object to two different names, _and_ the object is mutable (but not if it is immutable), mutating the object via one name will have the same effect on the object -- the same object, naturally -- bound to the other name. You know, maybe because I came to Python with no C experience, I never had trouble with the unexpected behaviour that so confused the original poster. It's just obvious. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Dennis Lee Bieber wrote: On Fri, 07 Sep 2007 12:19:12 -0700, Steve Holden [EMAIL PROTECTED] declaimed the following in comp.lang.python: Since it's only a matter of time before someone brings up the post-It analogy, let me cavil in advance about it. The thing I don't like about that particular pedagogic mechanism is that it always attaches the names to the objects. Fine... then visual the namespace as a box... Inside the box are the post-it notes -- attached to the ends of strings that then run to the physical object at the other end. This is getting clearer by the minute. ;) /W -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
gu wrote: hi to all! after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: [snip FAQ] Yes, basically you *created* a pointer. That's all that python has: pointers. When saying a = AnyOldObject() b = a then 'a' and 'b' are different /names/ for the /very same/ object (try a is b, or id(a)==id(b)). This is really a FAQ (once a week or so?), but for the life of me I can't find the right words for a google query. TO THE TROOP: What keywords would you attach to that question? /W -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
gu schreef: copyOfA = a now, in the second for cycle and in functionA() i only 'touch' copyOfA (altering it). copyOfA isn't a copy of a; it's a different name bound to the same object as a. You can verify that: id(a) and id(copyOfA) will return the same value. To make a copy of a (assuming a is a dict), you can do: copyOfA = dict(a) or copyOfA = a.copy() or more generally import copy copyOfA = copy.copy(a) Cheers, Roel -- If I have been able to see further, it was only because I stood on the shoulders of giants. -- Isaac Newton Roel Schroeven -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Fri, 07 Sep 2007 10:40:47 +, Steven D'Aprano wrote: Nor does it include peek and poke commands for reading and writing into random memory locations. I guess `ctypes` offers tools to write `peek()` and `poke()`. :-) Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On 2007-09-07, Peter Otten [EMAIL PROTECTED] wrote: Am Fri, 07 Sep 2007 10:40:47 + schrieb Steven D'Aprano: Python doesn't have any pointers. Thinking of python variables or names as pointers should get you a long way when trying to understand python's behaviour. But thinking of them as names bound to objects will get you further (and get you there faster). ;) As long as you keep in mind that python doesn't have pointers to pointers, and no pointer arithmetic either... -- Grant Edwards grante Yow! Hello... IRON at CURTAIN? Send over a visi.comSAUSAGE PIZZA! World War III? No thanks! -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Am Fri, 07 Sep 2007 10:40:47 + schrieb Steven D'Aprano: Python doesn't have any pointers. Thinking of python variables or names as pointers should get you a long way when trying to understand python's behaviour. As long as you keep in mind that python doesn't have pointers to pointers, and no pointer arithmetic either... Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Fri, 07 Sep 2007 11:46:38 +0200, Wildemar Wildenburger wrote: gu wrote: hi to all! after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: [snip FAQ] Yes, basically you *created* a pointer. That's all that python has: pointers. No, you are confusing the underlying C implementation with Python. Python doesn't have any pointers. CPython is implemented with pointers. PyPy, being written entirely in Python, is implemented with Python objects like lists and dicts. Jython, being implemented in Java, probably isn't implemented with pointers either -- although of course the underlying Java compiler might be. IronPython and Python for .Net, I have no idea how they work. Could be magic for all I know. (Probably necromancy.) Naturally, regardless of whether you are using CPython, IronPython, PyPy or some other variety of Python, the objects available to you include ints, floats, strings, lists, dicts, sets and classes... but not pointers. Nor does it include peek and poke commands for reading and writing into random memory locations. Python is not C, and it is not Basic, nor is it Forth or Lisp or assembler, and you shouldn't hammer the round peg of Python objects into the square hole of C pointers. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Sep 7, 3:07 am, gu [EMAIL PROTECTED] wrote: hi to all! Hi! after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: code a = {} for x in range(10): for y in range(10): a[x,y] = 0 copyOfA = a def functionA(x,y): print a[x,y], copyOfA[x,y] = * print a[x,y],copyOfA[x,y] for x in range(10): for y in range(10): functionA(x,y) /code now, in the second for cycle and in functionA() i only 'touch' copyOfA (altering it). as i don't touch the variable a, i expect it not to be affected by any change, but copyOfA acts like a pointer to a and altering copyOfA's values result in altering the values of a, so the result that i expect is: 0 0 * 0 0 * 0 0 * 0 0 * [..] but i get: 0 * * 0 * * 0 * * 0 * * [..] what's going on? thanks in advance. Welcome to Python! You might want to look at the documentation: http://docs.python.org/ And the tutorials: http://docs.python.org/tut/tut.html Leaping into python from another language without looking at the above documentation is not wise, since python has both a very different structure and a somewhat different philosophy from other languages. -- http://mail.python.org/mailman/listinfo/python-list
unexpected behavior: did i create a pointer?
hi to all! after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: code a = {} for x in range(10): for y in range(10): a[x,y] = 0 copyOfA = a def functionA(x,y): print a[x,y], copyOfA[x,y] = * print a[x,y],copyOfA[x,y] for x in range(10): for y in range(10): functionA(x,y) /code now, in the second for cycle and in functionA() i only 'touch' copyOfA (altering it). as i don't touch the variable a, i expect it not to be affected by any change, but copyOfA acts like a pointer to a and altering copyOfA's values result in altering the values of a, so the result that i expect is: 0 0 * 0 0 * 0 0 * 0 0 * [..] but i get: 0 * * 0 * * 0 * * 0 * * [..] what's going on? thanks in advance. -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Steven D'Aprano wrote: On Fri, 07 Sep 2007 11:46:38 +0200, Wildemar Wildenburger wrote: gu wrote: hi to all! after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: [snip FAQ] Yes, basically you *created* a pointer. That's all that python has: pointers. No, you are confusing the underlying C implementation with Python. I do not, as I have no clue of the C implementation :). I just thought I'd go along with the analogy the OP created as that was his mindset and it would make things easier to follow if I didn't try to forcibly change that. Please note that I had intended for the word 'created' to be in quotes rather than asterisks. I bit myself after I read my mistake online but then thought Who cares?. I should have, maybe :). And yes, I will admit that going along with that analogy isn't the best way to explain it. Grant Edwards in reply to Peter Otten makes it much clearer, I guess. /W -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
En Fri, 07 Sep 2007 05:07:03 -0300, gu [EMAIL PROTECTED] escribi�: after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: code a = {} for x in range(10): for y in range(10): a[x,y] = 0 copyOfA = a copyOfA is *NOT* a copy - it's just another name pointing to the SAME object as a. Python will never copy anything unless told explicitely. Read this http://effbot.org/zone/python-objects.htm -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Steven D'Aprano wrote: On Fri, 07 Sep 2007 11:46:38 +0200, Wildemar Wildenburger wrote: gu wrote: hi to all! after two days debugging my code, i've come to the point that the problem was caused by an unexpected behaviour of python. or by lack of some information about the program, of course! i've stripped down the code to reproduce the problem: [snip FAQ] Yes, basically you *created* a pointer. That's all that python has: pointers. No, you are confusing the underlying C implementation with Python. Python doesn't have any pointers. CPython is implemented with pointers. PyPy, being written entirely in Python, is implemented with Python objects like lists and dicts. Jython, being implemented in Java, probably isn't implemented with pointers either -- although of course the underlying Java compiler might be. IronPython and Python for .Net, I have no idea how they work. Could be magic for all I know. (Probably necromancy.) Naturally, regardless of whether you are using CPython, IronPython, PyPy or some other variety of Python, the objects available to you include ints, floats, strings, lists, dicts, sets and classes... but not pointers. Nor does it include peek and poke commands for reading and writing into random memory locations. Python is not C, and it is not Basic, nor is it Forth or Lisp or assembler, and you shouldn't hammer the round peg of Python objects into the square hole of C pointers. This seems to be obscuring the real issue for the sake of hammering an error in vocabulary. gu said Yes, basically you *created* a pointer. That's all that python has: pointers. and you took issue with that, ultimately saying the objects available to you include ints, floats, strings, lists, dicts, sets and classes... but not pointers. You are both right, and you are also both wrong. Python does indeed provide a rich set of strongly typed object classes, and so clearly to say Python only has pointers is strictly an error. However, this overlooks the fact that *all* names in Python, and *all* items in container objects (lists, tuples, dicts ...) hold references to objects. I mention this because it *is* significant to the semantics of assignment. From the point of view of a C programmer Python might actually look quite like a language in which all data objects had to be malloc'd, and the only variables were pointers to. Assignment (binding) in Python creates copies of references to objects, not copies of the objects themselves. I have deliberately omitted discussion of the automatic dereferencing that takes place in Python, thereby allowing us to treat names as though they contained objects, but the fact remains that names *don't* contain objects, they contain references to objects. If you want to regard a reference and a pointer as two different things then I guess that's your nit to pick. But I don't think the original assertions quite justified your scathing remarks about peek and poke. regards Steve -- Steve Holden+1 571 484 6266 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Skype: holdenweb http://del.icio.us/steve.holden --- Asciimercial -- Get on the web: Blog, lens and tag the Internet Many services currently offer free registration --- Thank You for Reading - -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
Grant Edwards wrote: On 2007-09-07, Peter Otten [EMAIL PROTECTED] wrote: Am Fri, 07 Sep 2007 10:40:47 + schrieb Steven D'Aprano: Python doesn't have any pointers. Thinking of python variables or names as pointers should get you a long way when trying to understand python's behaviour. But thinking of them as names bound to objects will get you further (and get you there faster). ;) True. Since it's only a matter of time before someone brings up the post-It analogy, let me cavil in advance about it. The thing I don't like about that particular pedagogic mechanism is that it always attaches the names to the objects. To me that blurs the fact that the names live strictly inside namespaces, and are destroyed (along with the references they make to other objects) when the namespace goes out of scope or otherwise ceases to exist (instance destruction being the obvious one). I only mention this because I too can be a pedantic little bugger when I want to be. Have a nice day. regards Steve -- Steve Holden+1 571 484 6266 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Skype: holdenweb http://del.icio.us/steve.holden --- Asciimercial -- Get on the web: Blog, lens and tag the Internet Many services currently offer free registration --- Thank You for Reading - -- http://mail.python.org/mailman/listinfo/python-list
Re: unexpected behavior: did i create a pointer?
On Fri, 07 Sep 2007 15:59:53 +0200, Wildemar Wildenburger wrote: I just thought I'd go along with the analogy the OP created as that was his mindset and it would make things easier to follow if I didn't try to forcibly change that. My reaction to somebody trying to reason with the wrong analogy is to teach them the right analogy, not to tell them they got it right when they actually got it wrong. My car won't start -- I must not have stirred the gasoline enough before baking it. Yes, that's right. It's very important to stir the gasoline fully so that all the ingredients are fully mixed. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list