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Logging
7:16One of the first things programmers do when software starts misbehaving is to stick in `print()` calls. This is great if you don't mind extra output, but there's a better way to get diagnostic info back from your app!
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We've gotten pretty good at printing
things out to the screen when we
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make scripts and games.
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Quite often though you don't want to print
everything out to the user,
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you want to collect information about how
something is running, or
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create a report when something blows up.
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This is where logging comes in.
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Let's go back to workspaces and see how to
use this really handy tool.
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So this dd_game.py is a slightly more
advanced version of
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the game that we built in Python
collections.
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The one where your in a maze, trying to
find the door.
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It draws the map,
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like before, but it shows some breadcrumbs
for where the player has been.
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So we'll scroll down here, and you can see
here we're,
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we're drawing like a dot if they've been
there, 'kay.
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So I'd like to know where the player,
monster and door start out but
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obviously I don't wanna tell the player
where the door and the monster are then
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they can just get away easily, right, so
this is a great time to use logging.
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To do this we have to import the logging
library.
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I'll do this to the top and since I'm
actually really picky
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I'm gonna put it before random because l
comes before r,
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alphabetical yeah, it's, it's kind of
ridiculous.
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So I can actually use it, so let's go
ahead and use it, and
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we'll just do logging.info You won't see
this, and
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then we'll do logging.warn OH NO.
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All right, so we're gonna save those and
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let's go down here, and run our script and
oh, look.
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There's our message, it says, OH NO.
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So that came out,
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but the one that said, You won't see this
didn't, didn't come out.
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We didn't get the info message let's go
and quit.
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So what can we do?
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First of all our, our info one didn't show
up we want these things to
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show up if we log them, and the second one
is that it printed directly to the screen,
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which means it'd be shown to the player
and we don't want to show it to
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the player, we want to print it to, maybe
a file cuz we gotta keep our secrets.
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We gotta keep our secrets, secret, right?
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So to do that, we're gonna use this basic
config method
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This is one place where Python's foolish
consistency kinda comes through.
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Some really old packages use camel
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case names You kinda just have to remember
it, or, or look it up each time.
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So let's do logging.basicConfig, and
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we're gonna give it a filename, and we're
gonna say game.log,
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and we're gonna give it a level and it's
gonna be logging.DEBUG.
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Okay, so the file name argument as
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you can probably guess tells logging what
file to log into.
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By default it does standard out which is
why things get printed.
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We want it to log into a file called
game.log.
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The path, the file name is relative, so
game.log is gonna be in the same directory
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as our script, if you wanted to go to say
/temp or something like that,
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then you'd put that in as well.
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So filename makes sense, but what's with
level?
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What does level mean?
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Well, level tells the logger what level to
start paying attention to,
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for messages, it'll ignore any messages
with a lower level.
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Well, what levels are available?
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Well, there are six log levels and
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their names make it pretty obvious what
they're for.
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They're critical, error, warning, info,
debug, and notset.
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You won't use notset very often, I'd
almost say never.
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Debug and info are for information about
the running of an application, so
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it's your debug information.
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This just massive stream of information to
keep track of what everything is doing.
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Info is like oh, this is a good thing to
monitor.
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Warning is for
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keeping track of questionable things that
happen during your app, like you know,
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maybe an exception occurs, and you want to
remember that it happened, and
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then error and critical are for when
things go horribly wrong.
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We want our logger to catch any and all
messages that have a level set.
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So we're setting the level to debug.
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Okay, so let's blog something.
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Let's go down here, to line 73, or so,
where's that at?
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[BLANK_AUDIO]
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It's down here.
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Yeah, 69 okay, close enough.
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We've got these three variables, monster,
door and player location.
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I wanna record what these things are, so
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we're gonna call logging.info, which if
you haven't noticed calling.info, .debug,
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.warning, whatever, that logs a message at
that particular level.
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So we're gonna say monster door and
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player, and then we're gonna call .format
on that, and
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we're gonna pass in monster, door and
player location, 'kay.
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So, that should log the starting position.
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Let's test it out.
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Right, cuz that's what we do, we test
things out.
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So python dd.game.
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All right, nothing got printed out, which
is exactly what we wanted.
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We don't wanna give the players an unfair
advantage, this time.
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So let's go ahead and quit actually, and
if we do an ls here,
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we see there's this file game.log.
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Now sometimes, things wont show up over
here right away, so
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let's just go ahead, and we'll just do cat
game.log and that'll print out game.log,
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and we see that we have an info message
logged from the root logger.
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Monster's at 0,1, door's at 0, 0, player's
at 1, 2.
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So this can be really tricky getting to
that door instead of hitting that monster.
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So, there's our message, that's great!
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I'm sure as you look through this
dd_game.py you'll find other places to
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add in more logging.
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You can log the current number of moves
that the players made,
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or if you made a version where the monster
moves,
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maybe log where the monster is after each
player move.
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As you can see, logging is a really useful
tool to use with your scripts.
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You can record an information passed in by
the user, and then ask for
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those logs if something doesn't work like
you expected it to.
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You can also log exceptions in your except
blocks.
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There's really nothing more frustrating
than trying to debug a script when you
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can't see what's going on.
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Actually that brings me to our next and
final topic the Python debugger.
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