Effective PyCharm Transcripts
Chapter: Debugging Python applications
Lecture: Concept: Debugging
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We have a whole variety of ways of viewing variable state. When we stop in the debugger obviously down here in the bottom right,
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we've got the watch list of variables. So we've got our creatures and if it's something interesting like a list we can expand
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it out and see more details. We've got our command, we've got the active creature turns out to be a bat
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of level three right now. So while this is fine, it doesn't really show you in context what's happening, doesn't show you here this value.
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We accept it from. The user is an A right on the line where we did the input and so on. So up here we can see way more information.
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We can see that we have this great text. This is not a comment, this is something that debugger puts here says here is
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a hero And the text representation of that is a creature. Gandalf of level 75. And we saw that we can even highlight it and pull
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it down basically the same interaction we have in the watch window Over here we have
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the active creature, that's a bat of level three and the color is important.
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Remember the hero is great because that's the value has always had since we've recently looked
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at it, but this creature has turned orange and that means it's changed last time through the loop, it was something else.
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Who knows what a toad or a dragon or whatever it is in our little story here, But now it's become a creature a bat of level three.
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And so the fact that it changed, orange tells you not just what is its value, but that it has somehow been updated over here.
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You can see there's this input that we got from the user, what did they type for this particular run of the game loop?
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They typed A so they're going to be attacking, What's going to do it here? Oh, Gandalf of level 75 is going to be attacking a creature bat of level
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three super cool. The way we can put all this together, seeing the values is great. But sometimes you might want to change the situation here
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We've asked the user to input something. What do you want to do? Attack run away or look around. They said attack like oh, you know,
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we really should have typed run away because that's the scenario we're trying to test.
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Well let's just change it. There's all these situations and programs that are hard to come up with exactly the right situation.
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So you can use the debugger to change it. So if we go down to the command and the variable window and choose set value
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or even to the gray part that the debugger put in and pull it down and say set value, we can change it.
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What if we put in [r] if we set this value and change into [r] what happens even though it says in the console up here. What do you want to do?
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Attack or runaway or look around, we set attack, but then all of a sudden the wizard has become unsure of his power and flees Why?
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Because we changed what happens. That's what happens if he were to run away.
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So very cool that we're able to sort of carefully control the flow for different situations to build up exactly what we want to test,
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It's pretty obvious you can watch variables, but you can also come over here and hit the plus and add a watch expression So I want to know any time.
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Is there an active creature whose level is greater than 15? Yes or no. We can watch that expression and you can put all sorts of
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interesting things like some database level call that says is the current user and admin yes
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or no. Right, That's not necessarily a property of the uh the current user
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object. Although maybe if it's not though you can still check that here in this evaluation watch area. So it's not just about watching variables,
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even though quite literally the title of the Windows variables really it's variables plus expressions.
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We saw the breakpoints are incredibly powerful here, we have two break points on our creature wizard game, we want to add a new one.
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You click in the gutter, Just the right of where the line numbers are,
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if you're showing them and that will create a default on off type of breakpoint is going to stop every time you hit it.
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We saw that if you right click on it though, you can actually change this to be something conditional. So imagine in this scenario we described before,
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I want to only hit the breakpoint if the user says R for run away. So the first bit of this test, if it's a else if it's it and or whatever,
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I'm going to put a breakpoint here and set the condition to 'cmd==r' right. Just a standard Python conditional. If that ever evaluates to true,
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we stop. So then we'll skip over all the other cases that are not running
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away scenarios and not have to deal with jumping out of the debugger too much.
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Remember this gives you auto complete and you can do pretty advanced Python right there.
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If you expand it, you can do even more like check the evaluate and log
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then print out some sort of computed message with details about what's happening every time the breakpoint hit. And if you uncheck suspend,
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that will basically become a breakpoint. That just logs out messages. Remember once you've got a conditional breakpoint,
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it has this little question mark by it. So normally it would just be a circle But now because that question mark,
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that means it's conditional. Be careful if you click on it without right clicking, you're just going to disable it.
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It will go away and well who knows what the condition was, but it's gone. So just be careful to not wipe these away unless you're sure
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you're done with them. Finally, if we turn this into a breakpoint that only logs messages,
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it turns yellow so you can see here we have suspend unchecked but evaluating log is turned on and we have this little F.
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String. The command is whatever they've typed the creature is the name of the active
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creature. And when we do this we get these little messages here like breakpoint reached The command is 'a' and the active creatures.
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The Tiger command is a active creature is a dragon and so on. Remember in my example I put like some stars or something to make it stand out
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because here without these boxes it's super hard to see what is the breakpoint and what is actually just program output around it.
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So be sure to add a little bit something to make these stand out.