On Thu, 31 Jan 2008 20:51:23 +0100, Helmut Jarausch wrote:
> Hi,
>
> the following code works fine
>
> def Helper(M) :
> return 'H>'+M
String concatenation is generally considered unpythonic, better use
string interpolation::
'H> %s' % (M,)
> class A(object):
> def __init__(self,Msg) :
> print Helper(Msg)
>
> B=A('ZZ')
Watch out your names -- they could confuse other Python programmers
introspecting your namespaces! Names bound to objects should generally be
lowercase (argument ``msg``, object ``b``, argument ``m``, function
``helper``). For details on what the Python community has agreed on is
"good style," see the `Style Guide <http://www.python.org/dev/peps/
pep-0008/>`_.
> but the Helper function is in the module's namespace.
Where's the problem? If it is "I don't want Helper to be visible", just
use this convention: "Names beginning with an underscore are private.
Better keep your fingers off."
> I'd like to put it into class A's namespace. Note, the Helper function
> doesn't need access to any instance attributes.
>
> The first variant
>
> class A(object):
> def Helper(M) :
> return 'H>'+M
> def __init__(self,Msg) :
> print Helper(Msg)
>
> doesn't work since Python is looking for a global function Helper (why?)
Because in the scope of the ``__init__`` function, the name ``Helper`` is
not bound. It then jumps out to the global scope.
> The alternative
>
> class A(object):
> def Helper(M) :
> return 'H>'+M
> def __init__(self,Msg) :
> print A.Helper(Msg)
>
> doesn't work either since now the first argument to A.Helper must be
> 'A'.
>
> So, isn't it possible to have a helper function in the namespace of a
> class without (the overhead of) passing a 'self' or a 'cls' parameter?
Of course it is! You can decorate certain functions with the
`staticmethod <http://docs.python.org/lib/built-in-funcs.html#l2h-69>`_
wrapper, which will do exactly what you wanted::
class A(object):
@staticmethod
def helper(m):
return 'H>%s' % (m,)
def __init__(self, msg):
print A.helper(msg) # or self.helper
HTH,
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