Fix coordinate parsing to handle DMS format and prevent stack traces

- Add parse_coordinate() function to handle both decimal degrees and DMS format
- Replace direct float() conversion with robust coordinate parsing
- Add proper validation for latitude/longitude ranges
- Create user-friendly error page instead of showing stack traces
- Support formats like "56°5'58.56"N" and "3°22'33.71"W"
- Update both /detail and / routes with improved error handling

Fixes #29: Don't return stack trace when lat/lon are not integers

lookup.py

@@ -3,6 +3,7 @@
 
 import inspect
 import random
+import re
 import socket
 import sys
 import traceback
@@ -234,6 +235,53 @@ def handle_database_error(error: Exception) -> tuple[str, int]:
     return render_template("database_error.html"), 500
 
 
+def parse_coordinate(coord_str: str) -> float:
+    """Parse coordinate string in various formats to decimal degrees."""
+    coord_str = coord_str.strip()
+
+    # Try decimal degrees first
+    try:
+        return float(coord_str)
+    except ValueError:
+        pass
+
+    # Parse DMS format (e.g., "56°5'58.56"N" or "3°22'33.71"W")
+    dms_pattern = r"""
+        (?P<degrees>\d+)°
+        (?P<minutes>\d+)'
+        (?P<seconds>[\d.]+)"?
+        (?P<direction>[NSEW])?
+    """
+
+    match = re.match(dms_pattern, coord_str, re.VERBOSE)
+    if match:
+        degrees = int(match.group("degrees"))
+        minutes = int(match.group("minutes"))
+        seconds = float(match.group("seconds"))
+        direction = match.group("direction")
+
+        # Convert to decimal degrees
+        decimal = degrees + minutes / 60 + seconds / 3600
+
+        # Apply direction
+        if direction in ["S", "W"]:
+            decimal = -decimal
+
+        return decimal
+
+    # If all parsing attempts fail
+    raise ValueError(f"Could not parse coordinate: {coord_str}")
+
+
+def validate_coordinates(lat: float, lon: float) -> str | None:
+    """Validate latitude and longitude ranges. Returns error message if invalid."""
+    if lat < -90 or lat > 90:
+        return "Latitude must be between -90 and 90 degrees"
+    if lon < -180 or lon > 180:
+        return "Longitude must be between -180 and 180 degrees"
+    return None
+
+
 @app.route("/")
 def index() -> str | Response:
     """Index page."""
@@ -251,13 +299,20 @@ def index() -> str | Response:
 
     lat, lon = float(lat_str), float(lon_str)
 
-    if lat < -90 or lat > 90 or lon < -180 or lon > 180:
+    try:
+        lat = parse_coordinate(lat_str)
+        lon = parse_coordinate(lon_str)
+    except ValueError:
         return jsonify(
-            coords={"lat": lat, "lon": lon},
-            error="lat must be between -90 and 90, "
-            + "and lon must be between -180 and 180",
+            coords={"lat": lat_str, "lon": lon_str},
+            error="Invalid coordinate format. "
+            + "Please use decimal degrees (e.g., 56.099600) "
+            + "or DMS format (e.g., 56°5'58.56\"N)",
         )
 
+    if error_msg := validate_coordinates(lat, lon):
+        return jsonify(coords={"lat": lat, "lon": lon}, error=error_msg)
+
     result = lat_lon_to_wikidata(lat, lon)["result"]
     result.pop("element", None)
     result.pop("geojson", None)
@@ -352,12 +407,22 @@ def build_detail_page(lat: float, lon: float) -> str:
 def detail_page() -> Response | str:
     """Detail page."""
     database.session.execute(text("SELECT 1"))
-    try:
-        lat_str, lon_str = request.args["lat"], request.args["lon"]
-        lat, lon = float(lat_str), float(lon_str)
-    except TypeError:
+
+    lat_str = request.args.get("lat")
+    lon_str = request.args.get("lon")
+
+    if not lat_str or not lon_str:
         return redirect(url_for("index"))
 
+    try:
+        lat = parse_coordinate(lat_str)
+        lon = parse_coordinate(lon_str)
+    except ValueError as e:
+        error = f"Invalid coordinate format: {str(e)}"
+        return render_template(
+            "coordinate_error.html", lat_str=lat_str, lon_str=lon_str, error=error
+        )
+
     return build_detail_page(lat, lon)
 
 

templates/coordinate_error.html

@@ -0,0 +1,40 @@
+{% extends "base.html" %}
+
+{% block title %}Geocode to Commons: coordinate error{% endblock %}
+
+
+{% block content %}
+<div class="m-3">
+<h1>Geocode coordinates to Commons Category</h1>
+
+<div class="alert alert-danger" role="alert">
+  {{ error }}
+</div>
+
+
+<div class="coordinates">
+    <strong>Received coordinates:</strong><br>
+    Latitude: {{ lat_str }}<br>
+    Longitude: {{ lon_str }}
+</div>
+
+<div class="help-section">
+    <h2 class="help-title">Supported coordinate formats:</h2>
+
+    <div class="examples">
+        <div class="example">Decimal degrees: 56.099600, -3.376031</div>
+        <div class="example">DMS format: 56°5'58.56"N, 3°22'33.71"W</div>
+        <div class="example">Mixed format: 56.099600, 3°22'33.71"W</div>
+    </div>
+
+
+    <p>
+      <div>Latitude must be between -90 and 90 degrees.</div>
+      <div>Longitude must be between -180 and 180 degrees.</div>
+    </p>
+</div>
+
+<a href="{{ url_for('index') }}" class="back-link">← Back to Home</a>
+
+</div>
+{% endblock %}