Re: User Access to the docstring of a property

2006-10-21 Thread Colin J. Williams 
George,

Thanks to Dietz and yourself.

Yes, I should have referenced the class, rather than the instance. 
However, for methods, the docstring is revealed for an instance.

Colin W.

PS It would help if someone could explain the use of @apply in the 
example Dietz gave.  The documentation gives no reference to @ or to 
decorators.

[EMAIL PROTECTED] wrote:
 Colin J. Williams wrote:
 Is there some way that the user can access the docstring specified for a
 property?
 
 Do keep in mind that the docstring is not guaranteed to be available.
 If
 the application is run with optimization turned on, docstrings are
 usually
 optimized out.  Docstrings are handy for reading code and maybe for
 debugging, but should not be relied upon for users, as opposed to
 developers.
 
 -- George Young
 
 Please see the example below:

 # propDocTest
 class A(object):
def __init__(self, value):
  self.value= value
def vGet(self):
  return self.value
V= property (fget= vGet, doc=Get Value.)

 a= A(22)
 print a.vGet()
 print a.V
 print a.V.__doc__ # this gives the docstring for the value returned
 help(a.V) # this gives the docstring for the class/type of
 the value returned

 Colin W.
 

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Re: User Access to the docstring of a property

2006-10-21 Thread Diez B. Roggisch 
Colin J. Williams schrieb:
 George,
 
 Thanks to Dietz and yourself.
 
 Yes, I should have referenced the class, rather than the instance. 
 However, for methods, the docstring is revealed for an instance.
 
 Colin W.
 
 PS It would help if someone could explain the use of @apply in the 
 example Dietz gave.  The documentation gives no reference to @ or to 

The decorator semantics are simple:


@a
@b(argument)
def foo():
pass

get translated to

foo = a(b(argument)(foo))

as a decorator is nothing but function that is called with one thing, 
and returns something else. or the same thing, by the way.

Now apply was important back then before the *args and **keywordargs 
shortcuts where introduced.

It basically takes a function as first argument, and possibly a list 
and/or dict, and invokes the function with that argumens in place.

So

def foo(a):
print a

apply(foo, [10])

works as simple as

foo(10)


locals() is a built-in that returns a dictionary which contains all the 
locally known names.

And property is a descriptor-creation-function, that has this signature:

property(fget, fset, fdel, doc)

Now we have all we need to decompose that neat property-creation-trick 
that doesn't pollute the class' namespace:

class Foo(object):
   @apply
   def bar():
  def fget(self):
  return self._bar
  doc = bar property
  return property(**locals())



What happens is this:

the decoration gets translated to this:

bar = apply(bar)

which does simply invoke bar, and assign the result to the name bar in 
the class.

invoking bar executes the property function, which is fed with the 
dictionary of the locals - coincidently named after the named arguments 
property takes.


What I really do love about this: it doesn't pollute the namespace.

Regards,

Diez
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Re: User Access to the docstring of a property

2006-10-20 Thread Diez B. Roggisch 
Colin J. Williams schrieb:
 Is there some way that the user can access the docstring specified for a 
 property?

You need to access it using the class, not an instance of it.

class Foo(object):

 @apply
 def prop():
 def fget(self):
 return 10
 def fset(self, value):
 pass
 doc = this is a docstring
 return property(**locals())

f = Foo()
print f.prop


print Foo.prop.__doc__

print f.__class__.prop.__doc__


Diez
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Re: User Access to the docstring of a property

2006-10-20 Thread georgeryoung 

Colin J. Williams wrote:
 Is there some way that the user can access the docstring specified for a
 property?

Do keep in mind that the docstring is not guaranteed to be available.
If
the application is run with optimization turned on, docstrings are
usually
optimized out.  Docstrings are handy for reading code and maybe for
debugging, but should not be relied upon for users, as opposed to
developers.

-- George Young

 Please see the example below:

 # propDocTest
 class A(object):
def __init__(self, value):
  self.value= value
def vGet(self):
  return self.value
V= property (fget= vGet, doc=Get Value.)

 a= A(22)
 print a.vGet()
 print a.V
 print a.V.__doc__ # this gives the docstring for the value returned
 help(a.V) # this gives the docstring for the class/type of
 the value returned
 
 Colin W.

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