Reading Tracebacks Without Panic

# Step 1 — Define the reusable `parse_age` function; its indented body describes what happens for each call.
def parse_age(text):
    # Step 2 — Start the operation that may fail so the expected exception can be handled explicitly.
    try:
        # Step 3 — Compute the right-hand expression and store its result in `age` for the next step.
        age = int(text)
    # Step 4 — Handle the expected failure path instead of allowing the program to terminate unexpectedly.
    except ValueError as exc:
        # Step 5 — Raise an explicit exception to signal that the required condition or input contract was violated.
        raise ValueError("age must be a whole number") from exc
    # Step 6 — Evaluate this condition and execute the indented branch only when the condition is true.
    if age < 0:
        # Step 7 — Raise an explicit exception to signal that the required condition or input contract was violated.
        raise ValueError("age cannot be negative")
    # Step 8 — Return the computed value to the caller so the result can be reused or tested.
    return age

# Step 9 — Iterate through the collection so the indented block is applied once for each item.
for value in ["34", "abc"]:
    # Step 10 — Start the operation that may fail so the expected exception can be handled explicitly.
    try:
        # Step 11 — Display the current value explicitly so the result/state can be inspected during execution.
        print(parse_age(value))
    # Step 12 — Handle the expected failure path instead of allowing the program to terminate unexpectedly.
    except ValueError as err:
        # Step 13 — Display the current value explicitly so the result/state can be inspected during execution.
        print(type(err).__name__ + ":", err)