VSCode provides powerful debugging capabilities for Python and other languages. This document steps through the process of debugging Python code.
In VSCode, rather than opening a single file, it is more usual to open a folder (from the File Menu). This is typically the source folder for a project. Make sure you have cloned the repo with these notes called python_intro. Then open the python_intro folder using the File Menu.
Next open a Python file. For these notes, open the file arithmetic.py in the folder Python. You can find this by selecting the Explorer in the top left:
When you open a Python file for the first time, a window may open prompting you to Select Python Interpreter. You should do this and select an appropriate interpreter. You'll see your interpreter in the bottom left. You can click on this to change the interpreter:
If you are using a virtual environment, see Chapter 12, you may need to navigate to the Scripts folder in your virtual environment and select python.exe in order to use the virtual environment interpreter.
You should now have arithmetic.py open in a window in VSCode. The top portion of it contains a number of function definitions. Near the bottom you will see the lines:
if __name__ == "__main__":
a, b = 3, 4
print(f"Testing multiply({a},{b}) = {multiply(a,b)}")
n = 5
print(f"Testing sum_to_n({n}) = {sum_to_n(n)}")When the arithmetic.py module is run, the top functions will be defined, and then the lines of indented code following this if statement will be executed.
To run this file in the VSCode Debugger, click in the arithmetic.py file. Then either press F5 or click on the left-bar Debug icon followed by Run and Debug like below:
You'll see the following menu displayed and select Python File:
This will open a terminal panel, call a long command that runs arithmetic.py, and display the output from it:
Try adding a break point to your code. Click to the left of line 4 and you'll see a red dot. This tells the debugger to stop when it reaches this line and before executing the line.
Now run the file again by pressing F5 and selecting Python File. You should see the code execution stop as below:
At this point you can hover the mouse over in-scope variables and see their values, such as x, y and result. Alternatively, you can select the Debug Console in the bottom panel (next to Terminal). In this window you can type Python commands in the current scope. That is, you can try out functions on x and y which are currently in scope like this:
This is very useful for checking that your functions are operating as expected and for figuring out whey they aren't. When you are ready to continue operation, press F5 again or the Continue icon:
To quit execution in the middle, press Shift-F5 or the Stop icon.