Finding the variables (read or write)

[Chris Kaynor]

On Mon, Jan 14, 2013 at 1:28 PM, Chris Angelico <rosuav at gmail.com> wrote:

> On Tue, Jan 15, 2013 at 6:48 AM,  <servekarimi at gmail.com> wrote:
> > I'd like to develop a small debugging tool for python programs.In
> Dynamic Slicing How can I find the variables that are accessed in a
> statement? And find the type of access (read or write) for those variables
> (in Python).
> > ### Write: A statement can change the program state.
> > ### Read : A statement can read the program state .
> > **For example in these 4 lines we have:
> > (1) x = a+b    => write{x} & read{a,b}
> > (2) y=6        => write{y} & read{}
> > (3) while(n>1) => write{} & read{n}
> > (4) n=n-1      => write{n} & read{n}
>
> An interesting question. What's your definition of "variable"? For
> instance, what is written and what is read by this statement:
>
> self.lst[2] += 4
>
> Is "self.lst" considered a variable? (In C++ etc, this would be a
> member function manipulating an instance variable.) Or is "self" the
> variable? And in either case, was it written to? What about:
>
> self.lst.append(self.lst[-1]+self.lst[-2])
>
> (which might collect Fibonacci numbers)?
>

And those aren't even covering the case that a, normally non-mutating,
method actually mutates. Consider the following class (untested):

class Test(object):
  def __init__(self, value):
    self.value = value
    self.adds = 0
  def __add__(self, other):
    self.adds += 1
    other.adds += 1
    return Test(self.value + other.value)

With that class,
 x = a + b
would mutate x, a, and b, presuming a and b are instances of Test.


>
> ChrisA
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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