# I/O

class StreamIter:

    '''Iterates over the lines in a stream.

    Unlike stream.__iter__(), doesn't wait for EOF to start returning lines.

    Offers curr() method.

    Forwards close() to the underlying stream.

    '''

    def __init__(self, stream):

        self.stream = stream

        self.line = None

    def __iter__(self): return self

    def curr(self):

        if self.line == None: self.line = self.stream.readline()

        if self.line == '': raise StopIteration

        return self.line

    def next(self):

        line = self.curr()

        self.line = None

        return line

    def close(self): self.stream.close()

class TracedOutputStream:

    '''Wraps an output stream, running a trace function on each string written

    '''

    def __init__(self, trace, stream):

        self.trace = trace

        self.stream = stream

    def write(self, str_):

        self.trace(str_)

        return self.stream.write(str_)

class LineCountOutputStream(TracedOutputStream):

    '''Wraps an output stream, making the current line number available.

    Lines start counting from 1.'''

    def __init__(self, stream):

        self.line_num = 1

        def trace(str_): self.line_num += str_.count('\n')

        TracedOutputStream.__init__(self, trace, stream)