Dynamic generation of doc-strings of dynamically generated classes

[Mikael Olofsson]

Hi!

I've asked Google, but have not found any useful information there.

Situation: I have a base class, say

class base(object): ImportantClassA ttribute = None

Now, I want to dynamically generate subclasses of base. That's not a
problem. However, I very much want those subclasses to have individual
doc-strings. More precicely, I want that important class attribute to be
reflected in the doc-string. That's the problem. The only way I've
managed to accomplish that is something like the following.
ImportantClassA ttribute = 7
docString = 'The case %s.' % (ImportantClass Attribute,)
exec('''class new(base): """%s"""
pass ''' % (docString,)) new.ImportantCl assAttribute = ImportantClassA ttribute
new.__doc__ 'The case 7.'

This works as intended. The subclasses do get the doc-strings I want
them to have, and I can live with this solution. But: This solution does
not strike me as especially beautiful or readable. My first naïve
attempt was instead the following.
class new(base): pass
new.ImportantCl assAttribute = 7
new.__doc__ = ('The case %(ImportantClas sAttribute)s.'

% new.__dict__)

Traceback (most recent call last):
File "<pyshell#3 5>", line 1, in -toplevel-
new.__doc__ = ('The case %(ImportantClas sAttribute)s.'
TypeError: attribute '__doc__' of 'type' objects is not writable

This is readable to me, but apparently not the way to go, since I'm not
allowed to replace the doc-string like this. I've also tried a number of
other ways, but they all stumble on similar reasons.

Any ideas? Am I stuck with the clumsy exec-solution, or are there other
ways to dynamically generate doc-strings of classes?

/MiO

[Alex Martelli]

Mikael Olofsson <mi****@isy.liu .se> wrote:
...

Any ideas? Am I stuck with the clumsy exec-solution, or are there other
ways to dynamically generate doc-strings of classes?

The best way to make classes on the fly is generally to call the
metaclass with suitable parameters (just like, the best way to make
instances of any type is generally to call that type):

derived = type(base)('der ived', (base,), {'__doc__': 'zipp'})
Alex

[George Sakkis]

"Mikael Olofsson" <mi****@isy.liu .se> wrote:

Hi!

I've asked Google, but have not found any useful information there.

Situation: I have a base class, say

>>> class base(object): ImportantClassA ttribute = None

Now, I want to dynamically generate subclasses of base. That's not a
problem. However, I very much want those subclasses to have individual
doc-strings. More precicely, I want that important class attribute to be
reflected in the doc-string. That's the problem. The only way I've
managed to accomplish that is something like the following.
>>> ImportantClassA ttribute = 7
>>> docString = 'The case %s.' % (ImportantClass Attribute,)
>>> exec('''class new(base): """%s"""
pass ''' % (docString,)) >>> new.ImportantCl assAttribute = ImportantClassA ttribute
>>> new.__doc__ 'The case 7.'

This works as intended. The subclasses do get the doc-strings I want
them to have, and I can live with this solution. But: This solution does
not strike me as especially beautiful or readable. My first naïve
attempt was instead the following.
>>> class new(base): pass
>>> new.ImportantCl assAttribute = 7
>>> new.__doc__ = ('The case %(ImportantClas sAttribute)s.' % new.__dict__)

Traceback (most recent call last):
File "<pyshell#3 5>", line 1, in -toplevel-
new.__doc__ = ('The case %(ImportantClas sAttribute)s.'
TypeError: attribute '__doc__' of 'type' objects is not writable

This is readable to me, but apparently not the way to go, since I'm not
allowed to replace the doc-string like this. I've also tried a number of
other ways, but they all stumble on similar reasons.

Any ideas? Am I stuck with the clumsy exec-solution, or are there other
ways to dynamically generate doc-strings of classes?

There's nothing specifically about doc-strings, but you can create and customise a whole class
dynamically:

def makeBaseSubclas s(impClassAttr) :
return type('new_%s' % impClassAttr,
(base,object),
{'ImportantClas sAttribute': impClassAttr,
'__doc__': 'The case %s' % impClassAttr})

new = makeBaseSubclas s(7)
new.ImportantCl assAttribute 7 new.__doc__

'The case 7'
HTH,
George

[Mikael Olofsson]

Alex Martelli wrote:

The best way to make classes on the fly is generally to call the
metaclass with suitable parameters (just like, the best way to make
instances of any type is generally to call that type):

derived = type(base)('der ived', (base,), {'__doc__': 'zipp'})

and George Sakkis said something similar.

Thanks, both of you. As I expected, there was a much better way than my
clumsy way. Anyway, this took me to section 3.3.3 in the reference
manual, and that will help me further.

Thanks again. Back to the keyboard!

/MiO