"""VarString.py
Define the VarString class that encapsulates a string with embedded
variables. For example:
from VarString import VarString
fromAddr = '"Samuel Clemens" <sam@marktwain.com>'
msg = VarString('''From: $fromAddr
To: $toAddr
Subject: A short message
Dear $toName,
Just a quick message to let you know that reports of my death
are greatly exaggerated.
Regards,
Samuel Clemens.
''')
# infoSource() returns a list of 2-tuples.
for toAddr, toName in infoSource():
sendMsg(str(msg))
"""
import types, re, sys
class VarString:
"""A string with embedded variables signified by $a $b etc."""
def __init__(self, string, immediate=None):
if type(string) != types.StringType:
raise TypeError
self.__immediate = immediate
if immediate:
self.__str = self.__process(string)
else:
self.__str = string
def __str__(self):
if self.__immediate:
return self.__str
else:
return self.__process(self.__str)
def __process(self, str):
r = re.compile("\$([A-Za-z_][A-Za-z0-9_]*)")
self.__caller_globals, self.__caller_locals = _caller_symbols()
newstr = r.sub(self.__embsub, str)
return newstr
def __embsub(self, match):
name = match.group(1)
if self.__caller_locals.has_key(name):
return str(self.__caller_locals[name])
elif self.__caller_globals.has_key(name):
return str(self.__caller_globals[name])
else:
raise NameError, "There is no variable named '%s'" % (name)
def _caller_symbols():
"""Global and local symbols from three calling frames back
Thanks to Itamar Shtull-Trauring for showing how this is done."""
try:
raise StandardError
except StandardError:
fr = sys.exc_info()[2].tb_frame
# We go back three calling frames: to __process() to
# __init__() or __str__() to its caller.
return (fr.f_back.f_back.f_back.f_globals,
fr.f_back.f_back.f_back.f_locals)
