Visual Debugging Webinar

• Debugging without PyCharm's debugger: print and pdb
• First use of the debugger (and the Cython speedups)
• Breakpoints
• Using the console/IPython at a breakpoint
• Conditional breakpoints
• All flavors of stepping through code
• Moving through stack frames
• Setting watches
• Attaching to processes
• Debugging during testing
• Extracting type information
• Django/Flask template debugging
• Viewing numpy/pandas data frames

Old-Fashioned Debugging

• Problem: Where is 0,0
• print statements
• import pdb; pdb.set_trace()

Visual Debugging

• Run program like normal, under the debugger
• Install Cython speedups
• Use breakpoint to solve first problem

Poking Around

• Problem: I want to use f-string f'Score: {self.score:02d}' but I'm not sure how
• Interactive would help
• Set breakpoint, then use Evaluate Expression
• Or, Console
• Install iPython and use it

Breakpoints

• Problem: What is that "delta_time" thing?
• Set breakpoint, observe value, click "Continue"
• Clear breakpoint, click "Continue"
• Problem: wrong filename, what directory am I in?
• Any Exception breakpoint

Stepping

• Problem: 50 coins at random positions
• Add for loop, but is random doing the right thing?
• Set breakpoint, start regular stepping
• Set breakpoint outside, and step into
• Ditto, step over
• Problem: How does Arcade collisions work?
• Add code then step into

Watch Expressions

• Problem: Are the number of coins actually decreasing?
• Set breakpoint in for coin in hit_list
• Add a watch expression: len(self.coin_list)
• Cause collision with multiple coins
• Step through and see the watch expression value

Stack Frames

• Problem: Which coin is in _set_center_x?
• In for loop, step into setting the x
• Move back up the stack
• Observe the watch expression and self.score

Debug During Testing

• Problem: TDD for "Don't show score when mouse is moving"
• Write a test to see if score goes up on collision
• It fails, I'm confused
• Use debugging
• Fix tests, clear breakpoint, re-run

Attach to Process

• Run game.py from command line
• Use "Attach to Process" and then debug it

Extract Type Information

• Preferences -> Build -> Python Debugger, checkbox for Collect

Django and Flask

• Open Flask project
• Set a breakpoint in a template

Extra Credit

• NodeJS/Chrome debugging
• Configuring Stepping
• Keyboard shortcuts for stepping
• Show Execution Point button in toolbar when you get lost
• Mute Breakpoints button
• Inspect watch value in separate window