getattr/setattr q.

[Paulo da Silva]

Hi!

In a class C, I may do setattr(C,'x',10).

Is it possible to use getattr/setattr for variables not inside
classes or something equivalent? I mean with the same result as
exec("x=10").

Thanks.

 

[Steven Bethard]

In a class C, I may do setattr(C,'x',10).

Is it possible to use getattr/setattr for variables not inside
classes or something equivalent? I mean with the same result as
exec("x=10").

If you're at the module level, you can do::

globals()['x'] = 10

If you're inside a function, you probably want to look for another way
of doing what you're doing.

What's the actual task you're trying to accomplish here?

STeVe

 

[Ben Finney]

In a class C, I may do setattr(C,'x',10).

That would set an attribute on the class C, shared by all instances of
that class.

If you want to set an attribute on an instance, you need to do so on
the instance object::
... def __init__(self):
... setattr(self, 'bar', 10)
... Traceback (most recent call last):
10

Is it possible to use getattr/setattr for variables not inside
classes or something equivalent? I mean with the same result as
exec("x=10").

"Variables not inside classes or functions" are attributes of the
module (so-called "global" attributes). Thus, you can use setattr on
the module object::
... this_module = sys.modules[__name__]
... setattr(this_module, 'bar', 10)
... Traceback (most recent call last):
10

 

[7stud]

Is it possible to use getattr/setattr for variables not inside
classes...?

What does the python documentation say about the definition of
setattr()?

 

[Steven D'Aprano]

Hi!

In a class C, I may do setattr(C,'x',10).

Is it possible to use getattr/setattr for variables not inside
classes or something equivalent? I mean with the same result as
exec("x=10").

Yes, but you shouldn't unless you really need to. You're better off
rethinking your algorithm.

If you think you really need to, you probably don't.

If you *really* think you really need to, you might.

Traceback (most recent call last):

globals()['x'] = 5
x

5


Note that there is also a function locals(), but it doesn't work as you
might expect:

.... locals()['x'] = 99
.... print x
....5

 

[Paulo da Silva]

7stud escreveu:

What does the python documentation say about the definition of
setattr()?

I didn't read the full python documentation, yet! I hope to survive
until then
In the meanwhile, I searched google for setattr python but all
references I could see were about X.foo type.

One more "RTFM culture" response ...

Thanks.
Paulo

 

[Paulo da Silva]

Steven Bethard escreveu:

Paulo da Silva wrote: ....

If you're at the module level, you can do::

globals()['x'] = 10

If you're inside a function, you probably want to look for another way
of doing what you're doing.

What's the actual task you're trying to accomplish here?

None. I asked just for curiosity. My problem has to do with the normal
case of a class or class instance. When I saw setattr/getattr as the way
to solve my problem I just felt curiosity on if and how it could be done
outside a class.

Thank you very much for your response.
Paulo

 

[Steve Holden]

Steven Bethard escreveu:

Paulo da Silva wrote: ...

If you're at the module level, you can do::

globals()['x'] = 10

If you're inside a function, you probably want to look for another way
of doing what you're doing.

What's the actual task you're trying to accomplish here?

None. I asked just for curiosity. My problem has to do with the normal
case of a class or class instance. When I saw setattr/getattr as the way
to solve my problem I just felt curiosity on if and how it could be done
outside a class.

Thank you very much for your response.
Paulo

You don't need setattr/getattr if you know in advance the name of the
attribute you need to access and you can get a reference to the object
whose attribute it is. So:

>>> import sys
>>> x = "Hello, Paulo"
>>> sys.modules['__main__'].x 'Hello, Paulo'
>>> globals()['x'] 'Hello, Paulo'
>>>

regards
Steve

 

[Steven Bethard]

You don't need setattr/getattr if you know in advance the name of the
attribute you need to access and you can get a reference to the object
whose attribute it is. So:

x = "Hello, Paulo"
import sys
sys.modules['__main__'].x

'Hello, Paulo'
a.k.a

'Hello, Paulo'

STeVe

 

[Steve Holden]

You don't need setattr/getattr if you know in advance the name of the
attribute you need to access and you can get a reference to the object
whose attribute it is. So:

x = "Hello, Paulo"
import sys
sys.modules['__main__'].x

'Hello, Paulo'
a.k.a

import __main__
__main__.x

'Hello, Paulo'

Indeed. Any handle on the right object will do.

regards
Steve

 

[Paulo da Silva]

Yes, but you shouldn't unless you really need to. You're better off
rethinking your algorithm.

I need it but inside a class. The idea is to pass an instance of a class
(think of something like a record but with some methods inside) with
"fields", whose names are not known in advance, to another class that
must handle those "fields" at the caller request given their names as
parameter strings.

Another use I am thinking of is in a xml driven program where some
parameters "foo=bar", read as strings, must be converted into internal
variables xxx_foo=bar. I have written a 1st draft using dicts but this
way it is much easier and readable.


Regards
Paulo