Re: Python scope is too complicated
Dan Bishop wrote: x = 17 sum(x for x in xrange(101)) 5050 x 17 Your example with generator expressions is interesting. Even more interesting is: def foo(x): y= (i for i in x) return y From the disassembly it seems that the generator is a code object but 'x' is not a cell variable. WTF? How do I disassemble the generator? Must look into this [ list comprehensions are different because they expand to inlined bytecode ] jf -- http://mail.python.org/mailman/listinfo/python-list
Re: Python scope is too complicated
jfj [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] def foo(x): y= (i for i in x) return y From the disassembly it seems that the generator is a code object What is type(foo([1,2,3])) ? but 'x' is not a cell variable. WTF? As I understand it, the object 'x' binds to is immediately used to create the generator object. The local name is just a dummy that is not part of the result. I believe that the above is equivalent to def foo(x): def _(z): for i in z: yield i return _(x) although I suspect that the implementation builds the generator more directly. Terry J. Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Python scope is too complicated
jfj wrote: def foo(x): y= (i for i in x) return y From the disassembly it seems that the generator is a code object but 'x' is not a cell variable. WTF? That's because x is not assigned to anywhere in the body of foo. The bytecode compiler optimizes away the creation of a cell in this case, just passing the value of x as an implicit parameter to the generator. How do I disassemble the generator? You'd have to get hold of the code object for it and disassemble that. There should be a reference to it in one of the co_consts slots, I think. -- Greg Ewing, Computer Science Dept, University of Canterbury, Christchurch, New Zealand http://www.cosc.canterbury.ac.nz/~greg -- http://mail.python.org/mailman/listinfo/python-list
Python scope is too complicated
Yeah, I know. It's the price we pay for forsaking variable declarations. But for java programmers like me, Py's scoping is too complicated. Please explain what constitutes a block/namespace, and how to refer to variables outside of it. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python scope is too complicated
On Sun, 20 Mar 2005 13:53:34 +0200, rumours say that Max [EMAIL PROTECTED] might have written: Yeah, I know. It's the price we pay for forsaking variable declarations. But for java programmers like me, Py's scoping is too complicated. Please explain what constitutes a block/namespace, and how to refer to variables outside of it. I presume you read 4.1 Naming and binding from Python reference manual. What constitutes a block is answered in paragraph 2, for example. Please come back with confusing / missing information in that chapter giving us a chance to improve the documentation. Cheers! -- TZOTZIOY, I speak England very best. Be strict when sending and tolerant when receiving. (from RFC1958) I really should keep that in mind when talking with people, actually... -- http://mail.python.org/mailman/listinfo/python-list
Re: Python scope is too complicated
Max wrote: Yeah, I know. It's the price we pay for forsaking variable declarations. But for java programmers like me, Py's scoping is too complicated. Please explain what constitutes a block/namespace, and how to refer to variables outside of it. Some may disagree, but for me the easiest way to understand python's scopes is this: In Python, there are only two scopes. The global and the local. The global scope is a dictionary while the local, in the case of a function is extremely fast. There are no other scopes. There are no scopes in the nested statements inside code blocks and there are no class scopes. As a special case, nested function definitions appear to be something like a nested scope, but in reallity this is detected at compile-time and a strange feature called 'cell variables' is used In order to write to a global variable from a function, we have to use: global var which notifies the compiler that assignment to 'var' does not make a new local variable, but it modifies the global one (OT: wouldn't global.var = 3 be nicer?). On the other hand, if we just want to read a global variable we don't have to say global var because the compiler sees that there is no assignment to 'var' in the function code and therefore intelligently concludes that it's about a global one. Generally, python sees everything as exec code in global_dictionary, local_dictionary In this case it uses the opcode LOAD_NAME which looks first in locals and then in globals (and actually, then in __builtins__) For functions it uses either LOAD_FAST for locals or LOAD_GLOBAL for globals. HTH jfj -- http://mail.python.org/mailman/listinfo/python-list
Re: Python scope is too complicated
jfj wrote: Max wrote: Yeah, I know. It's the price we pay for forsaking variable declarations. But for java programmers like me, Py's scoping is too complicated. Please explain what constitutes a block/namespace, and how to refer to variables outside of it. Some may disagree, but for me the easiest way to understand python's scopes is this: In Python, there are only two scopes. The global and the local. The global scope is a dictionary while the local, in the case of a function is extremely fast. There are no other scopes. This isn't true anymore, now that generator comprehensions have been added to the language. x = 17 sum(x for x in xrange(101)) 5050 x 17 -- http://mail.python.org/mailman/listinfo/python-list
Re: Python scope is too complicated
Hi All-- Dan Bishop wrote: In Python, there are only two scopes. The global and the local. The global scope is a dictionary while the local, in the case of a function is extremely fast. There are no other scopes. This isn't true anymore, now that generator comprehensions have been added to the language. x = 17 sum(x for x in xrange(101)) 5050 x 17 The equivalent in list comprehensions which currently allows the x to leak out into its containing scope is going away soon. Will that be another scope? Or are generator and list comprehensions only one scope? Metta, Ivan -- Ivan Van Laningham God N Locomotive Works http://www.andi-holmes.com/ http://www.foretec.com/python/workshops/1998-11/proceedings.html Army Signal Corps: Cu Chi, Class of '70 Author: Teach Yourself Python in 24 Hours -- http://mail.python.org/mailman/listinfo/python-list
