python use decimal as default type for non-integer numbers using macropy

macro_module.py

# macro_module.py
from macropy.core.macros import *
from macropy.core.walkers import Walker
macros = Macros()

@macros.expr
def expand(tree, **kw):
    return to_decimal(tree)

@macros.expr
def show(tree, **kw):
    print tree
    print real_repr(tree)
    print unparse(tree)
    return tree

@Walker
def w(tree, **kw):
    is_num = tree.__class__==ast.Num
##    if tree.__class__ == ast.Str:
##        print 'got  str'
    if is_num and not isinstance(tree.n, int):
        return to_decimal(convert_to_string(tree))
    return tree

@macros.expr
def t(tree, **kw):
    return w.recurse(tree)

def convert_to_string(a_num_node):
    new_node = ast.Str()
    new_node.col_offset = a_num_node.col_offset
    new_node.lineno = a_num_node.lineno
    # we should probable do something like:
    # with open(source,'rb') as f:
    #  line = f.readlines()[a_num_node.lineno]
    # i = a_num_node.col_offset
    # while c[i] in '0123456789.':
    #   i++
    # new_node.s = line[a_num_node.col_offset:i]
    new_node.s = str(a_num_node.n)
    return new_node

#Call(Name('Decimal', Load()), [Str('1.2')], [], None, None)
def to_decimal(tree):
    return ast.Call(ast.Name('Decimal', ast.Load()),
                [tree], [], None, None)

run.py

# run.py
import macropy.activate
import target

target.py

# target.py
from macro_module import macros, expand, show, t
from decimal import Decimal
def f(x):
    return t[5.4]
print repr(f(None))
print f(None).__class__

TO DO / problems / questions / etc:

1. is it possible to make a macro parse all the source instead of some "selection" ?
2. is it possible to obtain the original value of ast.Num node instead of its already processed float?