On Aug 25, 1:07 pm, Evan Driscoll <eva...@gmail.com> wrote:
> On Aug 25, 2:33 pm, Evan Driscoll <eva...@gmail.com> wrote:
>
> > I want to make a context manager that will temporarily change the
> > value of a variable within the scope of a 'with' that uses it. This is
> > inspired by a C++ RAII object I've used in a few projects. Ideally,
> > what I want is something like the following:
>
> Okay, so I think I actually got this with some consultation with a
> friend. Critiques?
>
> from contextlib import contextmanager
> import inspect
>
> def get_parents_var(offset, var):
> f = inspect.stack()[offset][0]
> if var in f.f_locals:
> return f.f_locals[var]
> else:
> return f.f_globals[var]
>
> def set_parents_var(offset, var, val):
> f = inspect.stack()[offset][0]
> if var in f.f_locals:
> f.f_locals[var] = val
> elif var in f_globals:
> f.f_globals[var] = val
> else:
> assert False
>
> @contextmanager
> def changed_value_tb(var_name, temp_value):
> # 1 is here, 2 will be the implicit next() function, 3 is the
> real caller
> offset = 3
> old_value = get_parents_var(offset, var_name)
> set_parents_var(offset, var_name, temp_value)
> try:
> yield None
> finally:
> set_parents_var(offset, var_name, old_value)
>
> x = 5
> print x # prints 5
> with changed_value_tb("x", 10):
> print x # prints 10
> print x # prints 5
Well, it wouldn't be a "can I rebind a variable using a with-
statement" thread if someone didn't post a solution that they thought
worked, but didn't test it on local variables.
Carl Banks
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