Dynamically create classes for spark-parser-framework

Peter Otten __peter__ at web.de
Mon Dec 15 20:59:40 CET 2003


Diez B. Roggisch wrote:

> I've got to create some spark-based parsers during runtime. For people not
> familiar with spark, a parser looks like this:
> 
> class MixFixParser(spark.GenericParser):
>     def __init__(self, start='p_start'):
>         spark.GenericParser.__init__(self, start)
> 
>     def p_rules(_, args):
>         """
>         p_start ::= p_op p_start
>         p_start ::=
>         p_op    ::= p_start lbracket p_start rbracket
>         """
>         return args
> 
> The framework looks for methods beginning with p_ and inspects its
> docstring for grammar rules.
> 
> I hope that the body of my p_rules will be uniform, so until now I'd like
> to have one paser baseclass like MixFixParser above, and then modify the
> docstring accordingly - only for one specified instance!
> 
> My first attempts failed due to
> 
> AttributeError: 'instancemethod' object attribute '__doc__' is read-only
 

If a writable __doc__ really is sufficient (which I doubt, while I know
nothing about spark):

>>> class T:
...     def demo(self, x):
...             print "demo(%r)" % x
...
>>> class Method:
...     def __init__(self, func):
...             self.func = func
...     def __call__(self, *args):
...             self.func(*args)
...
>>> t = T()
>>> t.demo = Method(t.demo)
>>> t.demo.__doc__ = "so what"
>>> t.demo.__doc__
'so what'
>>> t.demo("abc")
demo('abc')
>>> t.demo.__doc__ = "something else"
>>> t.demo.__doc__
'something else'

Maybe you can expand on this, e. g. doing self.method = Method(self.method)
for every method starting with "p_" in the constructor.

Peter





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