#!/usr/bin/env python
"""
dynimp.py - Import Modules On First Use
Author: Sean B. Palmer, inamidst.com
Example use: 
   import dynimp
   dynimp.dynimp('sys')
   print sys.version
"""

import inspect

class DynamicModule(object): 
   """DynamicModule(name, frame) -> new dynamic module."""
   cache = {}

   def __init__(self, name, frame): 
      DynamicModule.cache[self] = (name, frame)

   def __repr__(self): 
      name, frame = DynamicModule.cache[self]
      return "<DynamicModule '%s' at 0x%x>" % (name, id(self))

   def __import(self): 
      name, frame = DynamicModule.cache[self]
      module = __import__(name)
      dynmod = 'global %s\n%s = module' % (name, name)
      exec(dynmod, frame.f_globals, locals())
      return module

   def __setattr__(self, attr, obj): 
      module = self.__import()
      setattr(module, attr, obj)

   def __getattr__(self, attr): 
      module = self.__import()
      return getattr(module, attr)

def dynimp(*names): 
   frame = inspect.currentframe()
   for name in names: 
      yield DynamicModule(name, frame)

def test(): 
   global sys, os
   print "Dynamically importing"
   sys, os = dynimp('sys', 'os')

   print "Testing dynamically imported modules"
   print sys, '.'.join(str(n) for n in sys.version_info)
   print sys, sys.version
   print os.path.isdir('/')

if __name__=="__main__": 
   test()