free and nonlocal variables
In Python 3, free variable and nonlocal variable are synonym terms? Or is there a difference, like a free variable is a variable that is not a local variable, then nonlocal variables and global variables are both free variables? Thanking you in advance, Bartolomé Sintes -- http://mail.python.org/mailman/listinfo/python-list
Re: free and nonlocal variables
bartolom...@gmail.com於 2013年3月21日星期四UTC+8下午4時52分17秒寫道： In Python 3, free variable and nonlocal variable are synonym terms? Or is there a difference, like a free variable is a variable that is not a local variable, then nonlocal variables and global variables are both free variables? Thanking you in advance, Bartolomé Sintes In python the interpreter has to check 4 levels of dictionaries in the run time to perform an action. The for levels are: 1. object instance level 2. class level 3. local function level 4. global level. Objects created at level 1,2,3 can be returned to some other object in the run time. Thus a GC is available to save the trouble of tracking everything for the programmer in a complex system. -- http://mail.python.org/mailman/listinfo/python-list
Re: free and nonlocal variables
On Thu, 21 Mar 2013 01:52:17 -0700, bartolome.sintes wrote: In Python 3, free variable and nonlocal variable are synonym terms? Or is there a difference, like a free variable is a variable that is not a local variable, then nonlocal variables and global variables are both free variables? Free variable is a formal term from computer science. As far as I know, Python uses it in exactly the same way. A free variable is a variable in an expression or function that is not local (which includes function parameters) to that expression. So both global and non-local variables are free variables. def spam(x): def inner(): y = x**2 - 1 return x + y + z return inner() In inner(), both x and z are free variables, but y is not, since it is local to the inner() function. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: free and nonlocal variables
On 3/21/2013 4:52 AM, bartolome.sin...@gmail.com wrote: In Python 3, free variable and nonlocal variable are synonym terms? Yes, but that is idiosyncratic to Python. Or is there a difference, like a free variable is a variable that is not a local variable, then nonlocal variables and global variables are both free variables? I believe that is the usual definition, such as you would find on Wikipedia. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: free and nonlocal variables
On Thu, 21 Mar 2013 01:52:17 -0700, bartolome.sintes wrote: In Python 3, free variable and nonlocal variable are synonym terms? Free variable is a computer science term. A variable is free if it is not bound. E.g. x and y are free in x+y, x is bound and y is free in lambda x: x+y, x and y are both bound in lambda y: lambda x: x+y. IOW, a variable is free in an expression if the expression doesn't include whatever created the variable. In Python 3, the nonlocal keyword indicates that a name refers to a variable created in an outer function. Names are deduced as referring to local, nonlocal (outer) or global variables at compile time. If a name is a function parameter, then it's a local variable. If a function definition doesn't include an assignment to a name, or a global or nonlocal statement for that name, the name refers to a nonlocal variable (local variable in an enclosing function) if one exists, otherwise to a global variable. By default, the presence of an assignment causes the name to be treated as a local variable. If the variable is read prior to assignment, an UnboundLocalError is raised (even if a global or nonlocal variable exists with that name; the decision is made when the function is compiled, not when the assignment is executed). However, a global statement causes the name to be treated as a global variable, while a nonlocal statement causes it to be treated as a reference to a local variable of the enclosing function. Again, it is the presence of these statements during compilation, not execution of them at run time, which causes the name to be deduced as a global or nonlocal variable. -- http://mail.python.org/mailman/listinfo/python-list
Re: free and nonlocal variables
Nobody writes: On Thu, 21 Mar 2013 01:52:17 -0700, bartolome.sintes wrote: In Python 3, free variable and nonlocal variable are synonym terms? Free variable is a computer science term. A variable is free if it is not bound. E.g. x and y are free in x+y, x is bound and y is free in lambda x: x+y, x and y are both bound in lambda y: lambda x: x+y. IOW, a variable is free in an expression if the expression doesn't include whatever created the variable. And in (lambda x : x)(x) + x below, x occurs both free and bound. The free occurrences are bound by the outer lambda. (lambda x : (lambda x : x)(x) + x)(3) 6 -- http://mail.python.org/mailman/listinfo/python-list
