Question

If you have the following class:

class Foo(object):

    def __init__(name):
        self.name = name

And you use it like this in a file called check_foo.py

with Foo("naming it"):
    print Foo.name


with Foo("naming another"):
    print Foo.name

If you import check_foo and run dir(check_foo) you will only get a single check_foo.Foo module.

I know that PEP 343 mentions that you can do something like:

with Foo("naming it") as naming_it:
    print naming_it.name

And that it would get instantiated properly in check_foo as check_foo.naming_it but my question is it is possible to work around this and set the name dynamically.

I’m playing around with a proof of concept and want to know how far I can get with the above idea.

Could it be possible to name the instance using the string I am passing to Foo ?

Note: I am also aware about withhacks. Let’s not suggest I take a look at that 🙂

Answer 1

I’m not sure if this is the sort of hackery that you are looking for…

import inspect

class renameable(object):
  def rename_me(self, new_name):
    for stack_frame in inspect.stack()[1:]:
      frame_object = stack_frame[0] # frame is the first object in the tuple
      for (name, value) in frame_object.f_locals.iteritems():
        if value is self:
          old_name = name
          matched_frame = frame_object
          break
      if matched_frame:
        break
    if matched_frame:
      matched_frame.f_locals[new_name] = matched_frame.f_locals[old_name]
      del matched_frame.f_locals[old_name]

I doubt that this is a complete solution, but it does allow you to change one binding of a value to a name. It changes the name that is bound to the value which is closest to the call of rename_me. For example:

>>> import blah
>>> x = blah.renameable()
>>> x
<blah.renameable object at 0x1004cb790>
>>> x.rename_me('y')
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> y
<blah.renameable object at 0x1004cb790>
>>>

I’m not sure if this is better or worse than using withhacks but it does delve into a seldom explored module in the library.