setattr in class

[Bojan Mihelac]

Hi all - when trying to set some dynamic attributes in class, for
example:

class A:
for lang in ['1', '2']:
exec('title_%s = lang' % lang) #this work but is ugly
# setattr(A, "title_%s" % lang, lang) # this wont work

setattr(A, "title_1", "x") # this work when outside class

print A.title_1
print A.title_2

I guess A class not yet exists in line 4. Is it possible to achive
adding dynamic attributes without using exec?

thanks,
Bojan

[Fredrik Lundh]

Re: setattr in class

Bojan Mihelac wrote:

Hi all - when trying to set some dynamic attributes in class, for
example:
>
class A:
for lang in ['1', '2']:
exec('title_%s = lang' % lang) #this work but is ugly
# setattr(A, "title_%s" % lang, lang) # this wont work
>
setattr(A, "title_1", "x") # this work when outside class
>
print A.title_1
print A.title_2
>
I guess A class not yet exists in line 4. Is it possible to achive
adding dynamic attributes without using exec?

Move the for-in loop out of the class definition:

>>class A:

.... pass
....

>>for lang in ['1', '2']:

.... setattr(A, "title_%s" % lang, lang)

>>a = A()
>>a.title_1

'1'

A truly dynamic solution (using __getattr__ and modification on access)
would probably give you a more "pythonic" solution.

</F>

[Christian Heimes]

Re: setattr in class

Bojan Mihelac wrote:

I guess A class not yet exists in line 4. Is it possible to achive
adding dynamic attributes without using exec?

Correct, the class doesn't exist until the end of the class body. You
can either do it outside the class definition or you can use a metaclass.

Christian

[Bojan Mihelac]

Re: setattr in class

On Sep 12, 5:21 pm, Christian Heimes <li...@cheimes. dewrote:

Bojan Mihelac wrote:

I guess A class not yet exists in line 4. Is it possible to achive
adding dynamic attributes without using exec?

>
Correct, the class doesn't exist until the end of the class body. You
can either do it outside the class definition or you can use a metaclass.
>
Christian

thanks, can you give example on using a metaclass?

[Arnaud Delobelle]

Re: setattr in class

On Sep 12, 4:30 pm, Bojan Mihelac <bmihe...@gmail .comwrote:

On Sep 12, 5:21 pm, Christian Heimes <li...@cheimes. dewrote:
>

Bojan Mihelac wrote:

I guess A class not yet exists in line 4. Is it possible to achive
adding dynamic attributes without using exec?

>

Correct, the class doesn't exist until the end of the class body. You
can either do it outside the class definition or you can use a metaclass.

>

Christian

>
thanks, can you give example on using a metaclass?

class MoreMeta(type):
def __init__(self, name, bases, attrs):
more = attrs.get('more attrs')
if more:
for attr, val in more.iteritems( ):
setattr(self, attr, val)

class MoreObject(obje ct):
__metaclass__ = MoreMeta

class A(MoreObject):
moreattrs = {}
for i in '12':
moreattrs['title_' + i] = int(i)

>>A.title_1

1

>>A.title_2

2

>>>

--
Arnaud

[Michael Palmer]

Re: setattr in class

On Sep 12, 11:08 am, Bojan Mihelac <bmihe...@gmail .comwrote:

Hi all - when trying to set some dynamic attributes in class, for
example:
>
class A:
for lang in ['1', '2']:
exec('title_%s = lang' % lang) #this work but is ugly
# setattr(A, "title_%s" % lang, lang) # this wont work
>
setattr(A, "title_1", "x") # this work when outside class
>
print A.title_1
print A.title_2
>
I guess A class not yet exists in line 4. Is it possible to achive
adding dynamic attributes without using exec?
>
thanks,
Bojan

Is it really worth it? If the names of the attributes are only known
at runtime, why not just use a dict - that's what they are for. If you
want a dict plus some special behaviour, just write a class that
inherits from dict, or use UserDict.DictMi xin.