Displaying PDFs via the iPad

I used the iPad’s external screen output for the second time today (the first was trying out Chopper 2 with the TV as the screen and iPhone as controller) – this time not just as an experiment.

I have a set of revision worksheets (all PDFs that I inherited many years ago – I might have Word documents somewhere, but I’m not sure where).  Going over the questions in class, I can simply read the question out loud (but people don’t listen well enough and can’t ‘go back’ to it), or write it on the board (slow, handwriting code is problematic when you’ve got messy writing), but ideally it’s projected.

Mailbox flattening messages

The mailbox.py code does this to dump a message (e.g. when adding to a Maildir file):

def _dump_message(self, message, target, mangle_from_=False):
    # Most files are opened in binary mode to allow predictable seeking.
    # To get native line endings on disk, the user-friendly \n line endings
    # used in strings and by email.Message are translated here.
    """Dump message contents to target file."""
    if isinstance(message, email.Message.Message):
        buffer = StringIO.StringIO()
        gen = email.Generator.Generator(buffer, mangle_from_, 0)
        gen.flatten(message)
        buffer.seek(0)
        target.write(buffer.read().replace('\n', os.linesep))
    elif isinstance(message, str):
        if mangle_from_:
            message = message.replace('\nFrom ', '\n>From ')
        message = message.replace('\n', os.linesep)
        target.write(message)

(There’s a bit more that deals with other types of message).  Unfortunately, with some messages containing Unicode characters, this breaks with a UnicodeDecodeError:

Traceback (most recent call last):
  File "", line 1, in
  File "/usr/lib/python2.5/mailbox.py", line 245, in add
    self._dump_message(message, tmp_file)
  File "/usr/lib/python2.5/mailbox.py", line 203, in _dump_message
    buffer.seek(0)
  File "/usr/lib/python2.5/StringIO.py", line 106, in seek
    self.buf += ''.join(self.buflist)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 106: ordinal not in range(128)

The message does flatten with message.as_string() – or str(message) – without any problems.  I’m not really sure why mailbox.py doesn’t just use as_string(), rather than create a generator itself.  I’m also not totally sure where the error is coming from, especially since it happens inside of seek().

For now, I can just call mailbox.add() with msg.as_string(), rather than with msg directly, and it’ll work fine.  At some point, if I have time, I’ll revisit this and try and figure out if it’s a Python bug that should be reported.

D520 – Week Three

When planning the semester’s schedule for D520, I choose a few topics that seemed large and gave them a two-week time-slot.  One of these was chapter 4 of IronPython in Action, which covers duck typing, design patterns, and introduces the MultiDoc example that’s used throughout the middle section of the book.  One of the concepts that the course has always (at least, as long as I have known it) tried to push is the importance of design – not just user-interface design (although that’s both important and covered), but the importance of doing at least some planning before starting to write large amounts of code.  In the last couple of years, I’ve moved the course away from focusing on extensive formal design to also cover design patterns and testing (particularly automated testing, like unit tests).  Since this is such a major issue for the course, and since I planned on using MultiDoc as an example in class (I try to always have an example that continues on from week to week), this seemed like an obvious point for a two-week session.

D520 Week Two

Here’s my material from the second week of “D520: Programming” (in IronPython).  The students got some brief notes [PDF] and the first proper lab exercise [PDF].  The recommended reading this week was a post by Lukas Mathis about poor hardware design (and lessons to be learnt), and a post by Wil Shipley about tracking down a Delicious Library bug.  The notes are again in four sections: textbook chapters (this week chapter 3, which is fairly essential reading), tools (same as last week, although I also recommended IronPython 2.6b2), key points, and example code (from chapter 3 of the textbook).  The lab exercise is a modification of one from last year (when it was in Visual Basic) – I’m trying to keep as many of the previous lab exercises as possible, so that there is still a tiny bit of continuity between 2008 and 2009.