Fix the documentation of abstract methods.

[hivert]

Currently, the documentation of abstract methods has the following annoying problem, it doesn't appear when asked with "?" from a parent.

sage: P = Parent(category=CoxeterGroups())
sage: P.index_set?
Object `P.index_set` not found.
sage:                                

You have to write:

sage: CG = CoxeterGroups()
sage: CG.ParentMethods.index_set?
Type:           AbstractMethod
Base Class:     <class 'sage.misc.abstract_method.AbstractMethod'>
String Form:    <abstract method index_set at 0x219a320>
Namespace:      Interactive
File:           /usr/local/sage/sage/local/lib/python2.6/site-packages/sage/misc/abstract_method.py
Definition:     CG.ParentMethods.index_set(self)
Docstring:
       Returns the index set of (the simple reflections of) ``self``, as a
       list (or iterable).

Class Docstring:
       Constructor for abstract methods
[...]

This should be fixed.

CC: @nthiery

Component: documentation

Keywords: abstract methods

Issue created by migration from https://trac.sagemath.org/ticket/8571

[hivert]

Description changed:

--- 
+++ 
@@ -1,4 +1,29 @@
-Currently, the documentation of abstract methods has two annoying problems:
-- it doesn't appear when asked with "?" 
-- nothing says that they are abstract method in the doc.
+Currently, the documentation of abstract methods has the following annoying problem, it doesn't appear when asked with "?" from a parent.
+
+```
+sage: P = Parent(category=CoxeterGroups())
+sage: P.index_set?
+Object `P.index_set` not found.
+sage:                                
+``` 
+You have to write:
+
+```
+sage: CG = CoxeterGroups()
+sage: CG.ParentMethods.index_set?
+Type:           AbstractMethod
+Base Class:     <class 'sage.misc.abstract_method.AbstractMethod'>
+String Form:    <abstract method index_set at 0x219a320>
+Namespace:      Interactive
+File:           /usr/local/sage/sage/local/lib/python2.6/site-packages/sage/misc/abstract_method.py
+Definition:     CG.ParentMethods.index_set(self)
+Docstring:
+       Returns the index set of (the simple reflections of) ``self``, as a
+       list (or iterable).
+
+Class Docstring:
+       Constructor for abstract methods
+[...]
+```
 This should be fixed.
+

[nthiery]

comment:2

We should also think about if/how to merge with Python's new abstractmethods:

http://docs.python.org/library/abc.html