Every Python error you've ever struggled with has a visual cause. The call stack that overflowed. The index that walked one step too far. The variable that was never defined. Stop reading stack traces — watch your code hit the error step by step and understand it in seconds.
Why visual debugging works
Reading a stack trace tells you where the error occurred. But understanding why it occurred — and how to prevent it — requires seeing your code execute step by step up to the moment of failure. LearnBug runs your actual buggy code and shows you the exact line, variable state, and execution path that caused the error.
The LearnBug difference
Most debugging guides show you a fixed example. LearnBug lets you paste your own broken code, run it, and watch it fail step by step. You don't learn debugging by reading about errors — you learn it by seeing your specific code hit them.
Each page shows the error message, the exact cause, visual execution, and how to fix it permanently.
maximum recursion depth exceeded — Watch the call stack fill up frame by frame and see exactly when Python's 1000-call limit is hit.
list index out of range — Watch the loop index march past the last valid position and see exactly where the off-by-one happens.
unsupported operand type — Watch Python try to add a string and an integer and fail. See the type mismatch at the exact operation that caused it.
name 'x' is not defined — Variable used before assignment or outside its scope. Watch the scope chain and see exactly when the name lookup fails.
Accessing a dictionary with a key that doesn't exist. Watch the hash lookup fail and see how .get() and defaultdict prevent the error cleanly.
Calling a method that doesn't exist on that type. Watch the attribute lookup chain fail and understand why None objects cause this constantly.
Right type, wrong value — like int("hello") or sqrt(-1). See the invalid value reach the function and understand exactly why it's rejected.
The silent bug — a function returns None when you expected a value. Watch the None travel through your code until it causes a crash downstream.
Python can't find your import. Understand how Python's module search path works — and why your install or path is likely the real issue.
Your while loop never exits. Watch iterations pile up, variable states stay frozen, and see exactly which condition was never triggered to break out.
Python's whitespace matters. See how mixed tabs/spaces or unexpected indentation changes code scope — and watch the parser reject it at the exact line.
Division by zero — obvious in theory, invisible in loops. Watch your denominator become zero mid-execution and see exactly which iteration causes the crash.
The most common logic bug. Watch your loop run one iteration too many or too few — and see the exact boundary condition that made the count wrong.
Paste your broken code on LearnBug and watch it execute step by step until it hits the error.