Modern Python Projects Transcripts
Chapter: Your code editor
Lecture: Debugging Python code
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In the previous lesson, I showed you how to run a single Python file. This time I open a folder with just a single file there.
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But I want to show you what's the difference when you open a single file in VSCode versus when you open a folder that contains some files?
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When we go to this debug menu, you see that when you open the folder, you now have an option took create a launch.json file.
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That way, when we set up a launch configuration for our debugger, it will be persistent. So, let's click this and again we select flask and this
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creates a launched.json file inside our folder. It's actually inside the .vscode and here we have it,
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Here You can customize, how you want your flask application to be launched. The default values are good enough.
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But if, for example, you want to enable the debugger, then you would remove this argument. Now that we have this launch.json file.
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If we go back to the debug menu, you see that we have this launch configuration here, so we can simply press this green arrow to, launch our Debugger.
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And again, this started the simple development server. We can see the website by refreshing this page.
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As you can see, I've added a few more things to this file. So instead of displaying a static text,
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I'm displaying my name and then a random integer between 0 and 100 which will be
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our lucky number. I've added those two variables, so we can test how the debugging
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works. You can add a break point by clicking this red dot on the left side. So, let's put a break point on this line.
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Now, if we start the server again and we refresh the page, the code execution should stop at this line when it gets there.
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So let's try it. We have the server, we go here, you can see it's still loading, and we go back to VSCode
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and you have this indicator that we stopped here. On the left side, We can now see the locals and global variables.
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Only name is defined at this moment, but if we go one step down, you can see that we have the lucky number defined and then the name, under the
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variables menu. We have the watch menu, if you have a variable that you want to monitor, but it's not in the locals or in the global's.
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You can add it here to this WATCH menu, so, let's add another variable to our code. Let's re-run it. Let's actually add an expression to WATCH.
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Let's refresh the page and we go back to our break point, and now you can see, we can check. What's the value of this surname variable, under the WATCH
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We have a CALL STACK. So, if you have a complicated code that calls multiple
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functions, you would see the whole CALL STACK from the main function all the way down toward the break point is located.
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We only have one function, so it's not really useful. But if you have a code with a lot of things going on, cause that can be really helpful,
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and then finally you have list of break points because you can see we only have one in our app.py.
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But you also can insert break points when an exception is raised or when an exception
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is Uncaught, can also click here to deactivate all the break points or click here to add custom break point from this menu.
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And if you want to execute some Python code in your debugging session, you can goto this debug console.
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Here, you can run any Python expression, so you can inspect some of the existing variables. But you can also,
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for example, modify them. So, if we check the value of, name its Sebastian. And if we try to change it, you can see that now, in the local scope,
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name has changed to ‘Steven’. And if we continue the execution of this code and we go back to the browser you can see that our change has persisted.