TypeError: issubclass() arg 1 must be a class on Flask / Vercel

Question

I'm currently trying to host my Flask application on Vercel, but I keep getting the same error,TypeError: issubclass() arg 1 must be a class Full log:

[WARNING]   2024-03-01T18:22:28.551Z        Set both RATELIMIT_LIMIT and RATELIMIT_PERIOD in configuration. Default values are being used.
[ERROR] TypeError: issubclass() arg 1 must be a class
Traceback (most recent call last):
  File "/var/lang/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 850, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/var/task/vc__handler__python.py", line 31, in <module>
    if not issubclass(base, BaseHTTPRequestHandler):INIT_REPORT Init Duration: 2833.05 ms   Phase: invoke   Status: error   Error Type: Runtime.ExitError
Unknown application error occurred

I tried to change typing_extension to 4.5.0, typing-inspect to 0.8.0, andpydantic to 1.10.11, (as recommended here, but I still kept having the same issue.

Thanks in advance.

Answer 1

I managed to find an answer; I had configured vercel incorrectly. I used server.py as my main method, but vercel requires an index.py file. So I created an index.py file, that was a single line; from server import app. then vercel.json: Old:

{ "version": 2, "builds": [ { "src": "./server.py", "use": "@vercel/python" } ], "routes": [ { "src": "/(.*)", "dest": "/server.py" } ] }

New:

{ "version": 2, "builds": [ { "src": "./index.py", "use": "@vercel/python" } ], "routes": [ { "src": "/(.*)", "dest": "/" } ] }