Capstone Session Step 3: Refactor, Reviewed

A small, behavior-preserving refactor, requested after the fix went green: extract the per-token seconds calculation into its own named function, purely for readability -- no behavior change, so this step (co-12: small reversible steps) can be reverted on its own without touching the actual bugfix from step 2.

--- attempt2.py
+++ attempt3_final.py
@@ -1,4 +1,4 @@
-"""Capstone attempt 2 (fixed): parse_duration -- "1h30m"-style duration string to total seconds."""
+"""Capstone final: parse_duration -- convert an "1h30m"-style duration string to total seconds."""
 from __future__ import annotations
 
 import re
@@ -8,16 +8,23 @@
 
 
 def parse_duration(s: str) -> int:
-    """Parse a duration string like "1h30m" or "45s" into total whole seconds."""
+    """Parse a duration string like "1h30m" or "45s" into total whole seconds.
+
+    Raises ValueError if `s` is empty, has no valid tokens, or has any
+    unmatched/malformed trailing content.
+    """
     if not s:
         raise ValueError("duration string must not be empty")
     total = 0
     consumed = 0
     for match in _TOKEN.finditer(s):
-        value = int(match.group(1))
-        unit = match.group(2)
-        total += value * _UNIT_SECONDS[unit]
+        total += _seconds_for_token(match.group(1), match.group(2))
         consumed += len(match.group(0))
     if consumed != len(s):
         raise ValueError(f"invalid duration string: {s!r}")
     return total
+
+
+def _seconds_for_token(digits: str, unit: str) -> int:
+    """Convert one (digits, unit) token into whole seconds."""
+    return int(digits) * _UNIT_SECONDS[unit]

Review before accepting: touches only the function body's internal structure (extract-method) and docstrings -- no change to parse_duration's signature, its ValueError conditions, or the _UNIT_SECONDS table the previous step fixed. Diff-review checklist (co-15, mirroring ex-29 · diff-review-checklist): scope -- confined to the one file, no unrelated hunk; tests -- rerun below, not assumed; style -- adds a docstring, consistent with the rest of the file.

Run: python3 -m pytest test_parse_duration.py -q

Output (genuine, captured transcript):

.......                                                                  [100%]
7 passed in 0.00s

Verify: still all seven tests green after the refactor -- confirming the extract-method change was genuinely behavior-preserving, not just assumed to be. This is the final state committed to learning/capstone/code/parse_duration.py.

← Previous: Step 2: Fix, Green · Next: Trust/Verify Log →

Capstone Session Step 3: Refactor, Reviewed

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