Implement LedgerLite JSON expense tracker

Author: snafshar

python_practice/2026-10-15/ledgerlite/ledgerlite.py

@@ -0,0 +1,102 @@
+#!/usr/bin/env python3
+"""A tiny JSON-backed command-line expense tracker."""
+
+import argparse
+import json
+import os
+import tempfile
+from datetime import datetime, timezone
+from pathlib import Path
+
+
+def load_entries(path: Path) -> list[dict]:
+    if not path.exists():
+        return []
+    try:
+        data = json.loads(path.read_text(encoding="utf-8"))
+    except (OSError, json.JSONDecodeError) as exc:
+        raise ValueError(f"cannot read data file {path}: {exc}") from exc
+    if not isinstance(data, list):
+        raise ValueError("data file must contain a JSON list")
+    return data
+
+
+def save_entries(path: Path, entries: list[dict]) -> None:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    fd, temp_name = tempfile.mkstemp(prefix=path.name, dir=path.parent, text=True)
+    try:
+        with os.fdopen(fd, "w", encoding="utf-8") as handle:
+            json.dump(entries, handle, indent=2, ensure_ascii=False)
+            handle.write("\n")
+        os.replace(temp_name, path)
+    except Exception:
+        try:
+            os.unlink(temp_name)
+        except FileNotFoundError:
+            pass
+        raise
+
+
+def add_entry(entries: list[dict], amount: float, description: str, category: str) -> dict:
+    description = description.strip()
+    category = category.strip()
+    if amount <= 0:
+        raise ValueError("amount must be greater than zero")
+    if not description:
+        raise ValueError("description cannot be empty")
+    if not category:
+        raise ValueError("category cannot be empty")
+    entry = {
+        "amount": round(amount, 2),
+        "description": description,
+        "category": category,
+        "created_at": datetime.now(timezone.utc).isoformat(timespec="seconds"),
+    }
+    entries.append(entry)
+    return entry
+
+
+def build_parser() -> argparse.ArgumentParser:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--file", type=Path, default=Path("ledgerlite.json"))
+    commands = parser.add_subparsers(dest="command", required=True)
+    add = commands.add_parser("add", help="record an expense")
+    add.add_argument("amount", type=float)
+    add.add_argument("description")
+    add.add_argument("--category", default="uncategorized")
+    commands.add_parser("list", help="list all expenses")
+    commands.add_parser("summary", help="summarize spending by category")
+    return parser
+
+
+def main() -> int:
+    parser = build_parser()
+    args = parser.parse_args()
+    try:
+        entries = load_entries(args.file)
+        if args.command == "add":
+            entry = add_entry(entries, args.amount, args.description, args.category)
+            save_entries(args.file, entries)
+            print(f"Added {entry['amount']:.2f}: {entry['description']} [{entry['category']}]")
+        elif args.command == "list":
+            if not entries:
+                print("No expenses recorded.")
+            for index, entry in enumerate(entries, start=1):
+                print(f"{index:>3}. {entry['amount']:>9.2f}  {entry['category']:<14} {entry['description']}")
+        else:
+            totals: dict[str, float] = {}
+            for entry in entries:
+                totals[entry["category"]] = totals.get(entry["category"], 0.0) + float(entry["amount"])
+            if not totals:
+                print("No expenses recorded.")
+            for category, total in sorted(totals.items()):
+                print(f"{category:<18} {total:>9.2f}")
+            print(f"{'TOTAL':<18} {sum(totals.values()):>9.2f}")
+    except (OSError, ValueError, KeyError, TypeError) as exc:
+        print(f"Error: {exc}")
+        return 1
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())