Python - Python expresiones regulares

def _var(self, linea):

        regex = '(\\{(\\$(?:[a-z][a-z0-9_]*))\\})'

        rg = re.compile(regex ,re.IGNORECASE | re.DOTALL)

        m = rg.search(linea)

        if m:

            txt = re.sub(regex ,r'<?php echo \g<2>; ?>', linea)

            print txt

            return txt

        else:

            return linea

import re

def _var(linea):

    regex = '(\\{(\\$(?:[a-z][a-z0-9_]*))\\})'

    txt = re.sub(regex ,r'<?php echo \g<2>; ?>', linea)

    return txt

print _var("la variable {$variable} tiene un valor erroneo");