Function _line_pair_iterator

Lib/difflib.py:1547–1576

Yields from/to lines of text with a change indication. This function is an iterator. It itself pulls lines from the line iterator. Its difference from that iterator is that this function always yields a pair of from/to text lines (with the change indication). If n

()

                yield from_line,to_line,True

    def _line_pair_iterator():
        """Yields from/to lines of text with a change indication.

        This function is an iterator.  It itself pulls lines from the line
        iterator.  Its difference from that iterator is that this function
        always yields a pair of from/to text lines (with the change
        indication).  If necessary it will collect single from/to lines
        until it has a matching pair from/to pair to yield.

        Note, this function is purposefully not defined at the module scope so
        that data it needs from its parent function (within whose context it
        is defined) does not need to be of module scope.
        """
        line_iterator = _line_iterator()
        fromlines,tolines=[],[]
        while True:
            # Collecting lines of text until we have a from/to pair
            while (len(fromlines)==0 or len(tolines)==0):
                try:
                    from_line, to_line, found_diff = next(line_iterator)
                except StopIteration:
                    return
                if from_line is not None:
                    fromlines.append((from_line,found_diff))
                if to_line is not None:
                    tolines.append((to_line,found_diff))
            # Once we have a pair, remove them from the collection and yield it
            from_line, fromDiff = fromlines.pop(0)
            to_line, to_diff = tolines.pop(0)
            yield (from_line,to_line,fromDiff or to_diff)

    # Handle case where user does not want context differencing, just yield
    # them up without doing anything else with them.