Show errors, even in production.

main.py

@@ -2,19 +2,51 @@
 """Find photos on flickr for Wikipedia articls and contact the photographer."""
 
 import collections
+import inspect
 import json
+import sys
+import traceback
 import typing
 from urllib.parse import unquote
 
 import flask
 import requests
+import werkzeug
+from werkzeug.debug.tbtools import DebugTraceback
 
 app = flask.Flask(__name__)
-app.debug = True
+app.debug = False
 
 enwiki = "en.wikipedia.org/wiki/"
 
 
+@app.errorhandler(werkzeug.exceptions.InternalServerError)
+def exception_handler(e: werkzeug.exceptions.InternalServerError) -> tuple[str, int]:
+    """Handle exception."""
+    exec_type, exc_value, current_traceback = sys.exc_info()
+    assert exc_value
+    tb = DebugTraceback(exc_value)
+
+    summary = tb.render_traceback_html(include_title=False)
+    exc_lines = "".join(tb._te.format_exception_only())
+
+    last_frame = list(traceback.walk_tb(current_traceback))[-1][0]
+    last_frame_args = inspect.getargs(last_frame.f_code)
+
+    return (
+        flask.render_template(
+            "show_error.html",
+            plaintext=tb.render_traceback_text(),
+            exception=exc_lines,
+            exception_type=tb._te.exc_type.__name__,
+            summary=summary,
+            last_frame=last_frame,
+            last_frame_args=last_frame_args,
+        ),
+        500,
+    )
+
+
 @app.route("/")
 def start() -> str:
     """Start form."""