[myhdl-list] Conversion of class methods

[Christopher F. <chr...@gm...>]

I had put together a fairly generic (weak) MEP for class method 
conversion, http://www.myhdl.org/doku.php/meps:mep-108.  The following 
is a more in depth conversation/analysis of the items (I am aware of) 
that need to be handled to enable class method conversion.  The items 
discussed are:  The "self" argument, class attributes, and the extract 
hierarchy process.

The MEP was only intended to handle class methods and not arbitrary 
conversion of classes.

Handling the "self" argument
-----------------------------
If I naively send a class method to the conversion routines the method 
will fail to convert correctly.   It will fail because the "self" 
argument is treated as the first port (see the current MEP for an 
example).

Performing a quick test by searching for "self" in the argument list and 
ignoring the self argument will render the object method convertible. 
Adding these changes to
   _AnalyzeTopFuncVisitor.vist_FunctionDev(...) (_analyze.py)
allows a top-level class method and buried methods to be converted.  I 
have prototyped and created some tests which can be viewed here, 
https://bitbucket.org/cfelton/myhdl-0.8-dev-containers/overview (clone 
of the myhdl 0.8 dev, see notes at the end).

A couple *issues* with this approach!  Although the "self" argument is 
almost always used I don't believe its enforcement; the "first" argument 
can have any name.  A simple experiment demonstrates the object 
reference can be anything.

   >>> class Foo():
   ...     def __init__(this, self):
   ...             print("New foo, this, self %s" % (self))
   ...
   >>> f = Foo('bar')
   New foo, this, self bar
   >>>

A more generic identification would be required.  Ideally, you would 
like to identify the class method (distinguish the method from a 
function) and ignore the first argument, currently I do not know how 
this can be accomplished in the AST parsing (visiting).

Assuming this technical hurdle can be overcome, the class method 
conversion would be possible.  But ... this only takes care of the 
"self" argument, in addition the class/objects attribute access and the 
extract hierarchy need to be addressed/discussed.

Class attribute access
-----------------------
There are two types of attributes to consider.  The first a simple 
attribute (immutable?) which would simply hold a constant.  Example, the 
number of bits to have in a signal, etc.  Even these simple attributes 
would require changes.

The bigger issue is accessing convertible types (Signal) that are 
referenced through the object's attributes.  This issue is a can of 
worms and I was not intending to address this "feature" with this MEP, 
but a separate MEP was created, 
http://www.myhdl.org/doku.php/meps:mep-107, to address general class 
attribute conversion.

This brings up a couple questions:

   1. Should an initial class method conversion be added with the 
limitation: no class attributes can be accessed?  (baby steps)

   2. If no, then should the MEPs be changed so that 107 only addresses 
the other "containers" (if this is even desired) and 108 should include 
handling attributes?

Extracting the hierarchy
-------------------------
While experimenting it was noticed that class methods were not 
identified in the _extractHeirarchy.  The _extractHeirarchy uses a 
different approach to determine the functions and generators that are to 
be converted.  The approach, using the "profile" functions does not 
identify the class methods, only functions (?).  This breaks some of the 
features (e.g. user-defined code).  It needs to be determined if the 
"profile" parsers can handle extracting the class methods or if the AST 
parser will need to be used (light-weight version of the AST to only 
extract hierarchy)?  Thanks to Wesley for providing the examples with 
the user-defined code.

Closing remarks
----------------
Note, this work is preliminary, I have not made enough progress to 
present a complete working solution.  This post is to inform the group 
what I have done and some issues I have run into and to solicit 
feedback.  Any comments or suggestions welcomed and appreciated.  I 
intent to hack away at this and try to resolve the above issues, time 
permitting.

If you look at the commits in bitbucket be prepared.  One, I must have 
my editor to replace tabs with spaces.  In some cases more lines are 
modified than needed.  Two, I keep messing up mercurial and branches, 
extra commits to default that were not intended.  Both these mistakes 
make the commit diffs unusable.  At some point I will need a clean 
working clone, doh.

References
-----------
[1] http://docs.python.org/tutorial/classes.html