class TranscriptPrint(object):
    """Trap all output directed to stdout/err (e.g by print statements) and
    redirect it to a file.

    Subclasses may modify the default behavior by overriding the Hook* methods.

    Highly simplified from:
    http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/119404"""
    
    def __init__(self,fname='transcript',stream='stdout',start=False):
        if stream not in ['stdout','stderr']:
            raise ValueError,'stream must be "stdout" or "stderr"'
        self.orig_stream = None
        self.stream = stream
        self.fname = fname
        self._closed = False
        # Each instance starts with a clean transcript file
        try:
            os.unlink(fname)
        except OSError:
            pass
        if start:
            self.start()

    def hook_start(self):
        self.f = open(self.fname,'a')

    def hook(self,text):
        """hook must return whether to proceed with normal printing or not"""
        self.f.write(text)
        return True

    def hook_stop(self):
        self.f.close()

    def start(self,func=None):

        if self._closed:
            raise IOError("TranscriptPrint instance is closed.")
        
        if self.stream == 'stdout':
            sys.stdout.flush()
            self.orig_stream = sys.stdout
            sys.stdout = self
        else:
            sys.stderr.flush()
            self.orig_stream = sys.stderr
            sys.stderr= self
        self.hook_start()

    def stop(self):
        """Stop will stop routing of print statements through this class"""

        self.flush()
        if self.stream == 'stdout':
            sys.stdout = self.orig_stream
        else:
            sys.stderr = self.orig_stream
        self.hook_stop()
        
    def write(self,text):
        """override write of output stream.

        The hook may supress output or modify the text printed to stdout."""
        
        proceed = self.hook(text)
        if proceed:
            self.orig_stream.write(text)
            self.orig_stream.flush()

    def __getattr__(self, name):
        """pass all other methods to the original stream"""
        #print '---Getting:',name  # dbg
        return getattr(self.orig_stream,name)